Best match for my Bryston 4b3 amp ?

thanks !

*** ROGUE RP-5 !!!
The 6SN7 based LS-100 based on my experience owning both it and the 12AU7 based BHK will be "warmer" sounding. The closest you will get to that with the Rogue will be with very expensive NOS Mullard tubes or some Matsushita's. So it depends on the "signature" of your Bryston and the type of sound you are trying to achieve. 
No not "bright" but 12AU7’s are just not as "warm" as 6SN7’s as a general rule but there are both types of both so pick the one you like and then adjust the tubes based on your budget. But based on just using the "stock" tubes provided the generalization will probably be true. I've owned gear from both companies and they both provide great customer service.
I have the LS 100 and it's a great piece.  The only thing similar I've owned to compare it to is a Audio Research LS 26.  The LS 26 is in my 2nd system.

My LS 100 is powered by Rogue Audio M-180 monoblocks.  I've been considering trying out some SS amps and would be curious to hear your impressions if that's the direction you decide to go.

I don't think the LS 100 is "warm".  To me it's pretty neutral sounding, not "tubey" like some tube devices I've listened to.  The Rogue monoblocks also sound more like SS amps than they do tube amps.  I would expect their preamps to have a similar sound signature, but have no experience with them.

The guys at Rogue and also Dan Wright at Modwright are pretty easy to get a hold of.  I'd reach out to them and explain what kind of sound you're after if you can't demo the units locally.
I had a new RP5 for a year and a half.  Out of the box it sounded great with the stock tubes but really came into its own with NOS Mullard tubes.  It was a very quiet preamp with many options.   It was very dynamic sounding as well.  I ran it with an Odyssey Stratos Extreme and later with a Conrad-Johnson MF 2550 amp. 
I was about to respond to the OP but stereo5 took the wind out of my sails. I would not have guessed that the RP-5 would have been a good match for either of the amps mentioned. Insufficient voltage at its rated distortion to drive the MF 2550 and too high an output impedance to match the Odyssey. Just goes to show you personal preference can trump specs. There is no substitute for auditioning with your own equipment if you are trying to match a tube pre-amp to an SS amplifier. 
If I were shopping for a pre-amp for a 4B3, I would be looking for something capable of 2V rms at its rated distortion with an output impedance about 200 ohms or less to create my short list, then keep my money in my pocket till I could audition candidates.

Before I bought the RP5 preamp, I contacted Rogue and talked to the chief designer.  I read him the specs on the Odyssey amp and was told it would be an excellent match.  So  much for specs.  As a matter of fact, the Odyssey sounded better than the Conrad Johnson amp and I was quite sorry I sold the Odyssey and bought the CJ..  I also used the RP5 with the McIntosh MC152 amp and it sounded better than the CJ.  I went all McIntosh and upgraded the power amp and sold the RP5 for the Mac C2500 tube preamp.
I had a LS-100 for several years.  Excellent preamp with the right tubes.  Have heard the Rogue RP-5 a few times, but never in my system.