KEF blades 2 or Dynaudio C4?

Steve59, we have to agree to disagree, over the years we have seen large expensive speakers shoe horned into less then ideal rooms with sometimes surprisingly fantastic results.
The key is how the system is tuned and how the system is adjusted.
Systems which do have external subwoofers that are part of the system, speakers such as the Scaena Iso Arrays, which have adjustable gain for the woofers worked great in two of our clients rooms that weren’t large at all.

We demoed  the Paradigm Persona 9H a speaker capable of 22hz bass response in a rather ordinary sized hotel room again with fantastic results and the same thing with the Legacy Aeris.
With today’s higher end dsp based room corrections systems you can solve the biggest issue in hifi which is bass which can over load the room and become boomy and ill-defined.

Even rooms and systems without Dsp you can use bass traps and custom hemholtz resonators to tune out the worst offending frequencies.
Our general philosophy is big room big speaker, small room small speaker, but as illustrated careful system matching and tuning can many times overcome the perceived issues.
With the desire to have X product and its intrinsic sound qualities and strengths and weakness in your room and commitment to getting it right you can accomplish things that shouldn’t sound right sounding pretty awesome.

Dave and TroyAudio Doctor NJ

@ OP

     I´ve owned the original C4s almost since they came out and over the years have listened to some pretty well regarded speakers since then, (including but not limited to the original Blades, not the 2s, older KEFs, Avalon, Proac, Pass´active Rushmores,Harbeth, Martin Logan CLX, Raidho, Sonus Faber and others),when the upgrade itch unsettled  my tranquility and sense of satistfaction with what I already had acheived in putting together my sytem.
     In fact I was very interested in the Blades based on curiosity concerning their concentric driver and I must admit their great looks from an industrial design perspective. As always personal taste will influence opinion so let me describe mine. What I´ve noticed over the years is the tendency in hi end design is towards speed, ¨accuracy¨ ?, detail, resolution, resolution and more resolution. Definitely not my cup of tea since most recordings are not up to snuff to be held up so close to such inspection.
     Most of the above descriptions about the C4s seem to me pretty accurate. They do need volume turned up to sound their best and that requires plenty of current. Also needed is plenty of space for them to open up and project a huge soundstage with electrostatic like coheviseness and imaging. Bass can be pretty awesome, almost full range but not quite with one caveat. Unles they have enough space they will sound muddied and indistinct as Atkinson described in his review. Not only that but the midrange and treble will suffer as a result. I wonder why he even bothers to review full range speakers with his obvious limitation in room size.Many find their treble response subdued, specially compared to the ilk of  metalic or ceramic tweeters. Personally I was convinced by the Esotar tweeter ever since I heard them on Sonus Faber Extremas. In fact only some ribbon or plasma tweeters I consider superior and then there are implications in integrating those with drivers of different materials but that is totally different matter.
     But summing it up, the main reason I have kept my C4s thru the years is as their publicity used to push is their total honesty to the source. As an example there is an older late 50´s mono recording of a string quartett that I use to evaluate string tone which was obviously recorded using tubes. Well you would swear my system was tube based which it is not. SS pre and 400 watt mono amps !
     So as you can see I´m pretty biased towards the C4s but based on your described room conditions I´m pretty sure they are not for you at this time. I´d look more at different the Harbeth offerings, all great speakers at their and I stress reasonable price points or just keep your speakers that seem to satisfy you. Changes are not always for the best.
     On a further point, has anyone noticed that KEFs top of the line $150,000 USD Muon is a total ripoff of the C4s cabinet design ?

@mountainsong 
At the onset of his recent sales novella, he asked me “do you think.......”

I simply felt compelled to answer that question and to your point regarding dealers I totally agree, absolutely necessary. However, we don’t need a constant barrage of salesmanship dispensed under the guise of experience and audio wisdom. The best dealer/members posting here don’t behave like a self absorbed know it all. Atmasphere, Audioconnection and Ramtubes illustrate my point. 

Carry on. 

Forgot to mention sealed cabinets such as ATCs may be worth your while for consideration as they integrate more favorably than ported designs in smaller rooms.

Why on earth have you restricted yourself to only these two polar opposites?

You've got very different aesthetics being presented. The aluminium the Kef driver is composed of never really goes away as a slightly astringent colouration (despite  Kef's claims) & the C4s can easily go too far in the opposite direction. There are plenty of sweet spots between the two for you to consider - that cry out to be.  This Magico with an asking (Its the second time on AG & a lower price is certainly obtainable) of almost identical to the retail of the C4 platinum but with no tax, is engineered to a far, far higher level.  It was 90 K a decade ago & would be 6 figures plus now if new. >
   https://www.audiogon.com/listings/lis9460g-magico-m5-speakers-full-range
It's a super & turbocharged version of what Dynaudio would've made with similar drivers if they had a Magico sensibility & cost no object approach.

The best reviewer at The Absolute Sound gave it the kind of review no Dynaudio would've received from him >
http://www.theabsolutesound.com/articles/tas-196-magico-m5-loudspeaker/
If you want metal drivers made with far superior materials instead - then Focals latest beryllium tweeters are a clearly superior way to go.  Two choices available right now are -
https://www.audiogon.com/listings/lis9461b-focal-maestro-utopia-iii-full-range & for a huger savings -
https://www.audiogon.com/listings/lis93i6b-focal-sopra-n-2-full-range