MP150 or MP200

The mass of my Project 1 expression 2 carbon fiber tonearm is around 8.6 grams which I understand is on the medium side .

It’s pretty light for a modern world of tonearms

I like the MP110 very much . It’s a very coherent and controlled sound that hardly ever irritates . Its bass is not the most powerful or tight but is in line with the sound spectrum of the cartridge .

Look at the specs, this is entry level cartridge, the diamond is not even "nude", it’s bonded diamond - do you know what does it mean? If you like Nagaoka do yourself a favor and upgrade to the higher model (or find a much better cartridge for the same money). Nagaoka is not even a perfect match for your tonearm I believe, you could check with Hi-Fi Test LP for tonearm/cartridge resonance frequency.

The reason why you like MP110 is probably lack of experience with other MM cartridges.

But do not afraid to buy a better cartridge, each Nagaoka model is step up, for more money you will get "nude" diamond and boron cantilever, for even more you can get a better stylus profile instead of elliptical.

You know when someone mentioned vintage cartridges I thought of the same thing and up to where I know all cartridges must have some type of suspension as what then supports the cantilever .

Case in point , the mentioned Sony cartridge , when I investigated it goes all the way back to the 70s . I personally would never buy a cartridge that has been sitting on a shelf for 5 decades no less !

We have so many members on this forum (including myself) who’re using vintage cartridges (MM or MC) along with very expensive modern cartridges. If you think that buying a new $5000 MC cartridges you are free of suspension problems then you’re wrong and it’s primarily depend on material used by a cartridge designer. If you think that "all modern" is better than could you please explain me why people are using an old drivers in their speakers, a very old nos tubes in their new high-end amps, vintage turntables paired with modern high-end equipment ?

The best MM cartridges designed in the 70s/80s because it was a hey day of MM technology. Nowadays most of the people have no idea what is a phono cartridge, but for some reason you think that modern MM are any better?

Using over 60 reference class vintage MM/MI cartridges from the 70s/80s I have’t seen more than 2-3 samples with dried or softened rubber suspension. When there is a problem with suspension, a cartridge body lay down on the record in 20 seconds with recommended tracking force (this is very easy to check before buying, and every honest seller will do that for you). If you can’t see this problem then suspension is fine. The rest is a fairy tale to scare people and force then to buy modern junk for higher price. A used audio market is pretty strong and always will be strong (Lightly used or NOS is a matter of luck) @mcmvmx

I tried various samples of SONY XL-50 and never seen this model with softened rubber suspension.  

Late to the party but I have both the mp110 and the mp150.
The 150 is an audible improvement over the 110.
However I bought mine way before the big price hikes so not sure as I now would say it is the way to go.
I have heard the 200 is quite a bit better than the 150 and obviously the 500 is the grail but at what price now!
Pre price rise I would have said it was a no brainer but at $500 for the mp200 there is a LOT of competition.

Maybe look at comparable priced AT carts or Hana.

mcmvmx, You are right. Your arm is to light for the Nagaoka as it stand but, you can add mass to the tonearm. There are head shell weights and special screws of various masses. I always have to tune my arm a little to get it just right. I feel the same way you do. I would never by an old cartridge. I've used many of them back in the day and there is nothing special there. Modern cartridges are better in every way. Materials science has advanced dramatically since the 70s and 80s. 
The Ortofon 2M series has a much higher compliance. The Clearaudio MMs a little lower so you would have to add a little weight. Another cartridge that gets very little air play in the States in the Goldring 1012 GX
It is a high compliance, high output MM with a Gyger II stylus. Perfect for your arm. 

but for some reason you think that modern MM are any better?

Where did I say that ? I never said that . I said that cartridge suspensions can change over the years . Thats it 
 Nothing more . Plus I know MM cartridges as I have been an avid audiophile for almost 50 years . All my favorite equipment are old timers as Dalquisht DQ 10 , Spica TC 50 , DCM time windows . Mac 225 , Dynaco 416 with capacitance supply . Linn LP12 , Systemdek x2 , Heybrook Turntable , AGI preamp and many more . Don't jump to conclusion and read carefully my friend . Plus I stand by my original argument . It's true,  cartridge suspension hardness can change over the years . Even temperture changes on a new cartridge can change its performance on a day to day basis .