I paid $329 for a new MMF-2.2 and if I had a chance to do it over, I would probably stay with my MMF-2.2 (I haven't tried the Carbon). Adjustable VTA is important to me (I like playing with TT tweaks). The tonearm isn't carbon fiber, but, I'm quite impressed with its abilities. Also, I think it's a tad longer than the Carbon arm. I have the motor isolated on it's own little platform to keep vibration from bleeding into the plinth (which IMO seriously steals away nuances of sound from the vinyl grooves). I hear the Carbon has new vibration absorbing pads, however, I'm pretty pleased with my MMF 2.2 tweak. I hear absolutely no vibration between LP tracks.
I also have the Pro-Ject speedbox II and never used the factory cartridge. I use a Nagaoka MP-200 MM cart.
If adjustable VTA doesn't matter to you, then, perhaps the Carbon for that Carbon fiber tonearm and the new motor vibration isolation feature. I don't believe I've seen any negative reviews from Carbon buyers so far.
I wish they would offer a metal sub platter upgrade for these types of tables (like Rega has)