I'm by no means a good piano player (I would say not even competent), but I do love jazz piano (and Ye Olde stuff too ). I have the Steinway D and the K2 and since v6 the K2 has become much more interesting to me (but it's hard to escape the D - keep going back). I have the Kremsegg 2 pack ("ye olde pianos") and I rather like using them as well (for anything - don't get stuck into thinking in terms of modern piano only). I particularly like the Frenzel and the Bechstein (in the Kremsegg 2 pack).
With the sale on I suspect I will not be able to resist the Bluethner for long : hard to not find that sound attractive for jazz. The Steingraeber is also on my list (OK, they're all on my list, but those are the top suspects).
I find that since v6 (and the 6.5 update) I'm finding far more scope in the Steinway and K2 than I had been. I have no idea why, but they seem to have a lot more richness and variety in them (via customization and microphone/reverb settings) than they had before. The K2 used to sound a little artificial in the range just below middle C and now it sounds really a lot more natural. I've noticed since v6 that the number of FXPs being made seems to have dropped off - I think Modartt have really nailed down the realism to the point where FXPs aren't needed as much - YMMV.
For jazz I think you should consider upgrading to Standard (from Stage). You get the microphone placement and other tweaking features and I really think the microphone settings are a huge thing - it just changes the sound so much it's hard to describe until you play around with it. I have not regretted upgrading from Stage to Standard at all - just the microphone settings makes it worth it, IMO. The ability to load full FXPs and the impulse reverb features and tweaking make it a must have - more so than additional instruments.
Version 6+ has really changed my wishlist. The sounds have evolved to the point where there isn't much "missing" (that I can tell) and instruments I didn't use much (like the K2) are now really getting a lot more attention. I think I've spent more time with the K2 than the D since v6.
If you're not upgrading to Standard (do first, IMO) then consider the Kremsegg 2 pack (Frenzel and Bechstein 1899 - personal bias) or the Bluethner Model One (probably better for jazz).
StephenG