2.5-->2.6 is not worth the $250
256vram is the max that you will benefit from the 8600m gt card BUT 512mb vram wont hurt for better driving external monitors.
I've owned them all and now back on a 17" hi res mbp again for the 3rd time!! IMHO something about how the 17" mbp runs as a whole machine feels a bit faster than the 2.4ghz ,2.5ghz ,2.6ghz 15" mbp. I dont know if the mother board can take more heat or the cores can clock up faster but something about how the gui runs on osx seems alot more fluid to me even without using the mbp in external monitors.
To me I see some difference.
I've owned the 15" 2.4Ghz mbp last years merom with 256vram for 9 months (sold it) and bought the 15" 2.5ghz mbp and exchanged it due to the left speaker noise issue for the 2.4Ghz penryn and after a week and a half (thought it was a bit slow compared to the 2.5Ghz model with the 512mbvram overall it does feel slower on the 2.4Ghz model also left speaker making the hiss/static noise) and then exchanged to a 2.6Ghz penryn mbp with 512mb (some charging issue and that same hiss/static noise on the left side where the magsafe resides of the speakers and then to the 17" hi res 2.5Ghz (sold it on ebay) moved back to the 15" mbp 2.5Ghz thinking the hissing noise was fixed and then exchanged it for the 17" hi res 2.6Ghz model but had a buzzing screen issue so exchanged it for the 15" 2.5Ghz penryn mbp and that one was fine except the left speaker still (I noticed by now that all the 15" mbp has this left speaker hissing/static noise when the magsafe is connected) but somehow the apple store messed up with the correct serial numbering and long story short didnt charge me a restocking fee that I was ready to pay today and exchanged it for 17" hi res 2.6Ghz mbp (Perfect! Finally no left speaker static/hiss noise like all the 15" penryn that I went through and no lcd buzz noise like the previous 17" I had!).
And to me the 17" feels a bit faster overall (all model mbp's had the same hitachi travelstar 7k200 hdd installed + 4gb of crucial ram. Amazingly I didnt pay any restock fee!! =D I'm stopping with this 17" 2.6Ghz model for a good 3-4 years now.. its so perfect!
I'm not just saying because I'm biased or own the 17" even on previous forums I've gave advice that the 17" did feel overall faster even while owning the 15" mbp.
P.S... I've been through the exchanges of hell and it concluded with 2 different apple stores (I live by 2 just 15 minutes and 20 minutes apart from the two) and no restocking fee!! The managers are more like get it exchanged and get the line moving kind of deal. But now they've seen enough of me in each stores and I've seen enough of them as well and finally done and keeping this perfect 17" hi res mbp!
Just to be clear the 17" mbp doesnt make the hissing/static noise when the magsafe is connected from the left speaker or the right speakers. Also I noticed that some of the 15" mbp I had made some buzzing noise from the right speaker and one of them on the left as well, I was kind of annoyed but not that much. But I have to say the 17" hi res models except one that had a high pitch screen buzz noise has no other issues, quiet fan, very fast, runs very cool, evenly lit screen (more so than the 15"), no left speaker static/electric noise and the speakers sound golden!
The exchange started out with a 1.6Ghz mba and it had some weird white line issues as well no restock fee lol. I think this month I went through about 10 mbpS!! 1 selling on ebay and me loosing some $$ on it though but then it had a dead/stuck pixel that I really hated on it but the buyer didnt seem to mind it for a couple hundred less on the mbp =/.
And from my sig you can tell that I've owned the 2.8 8 core mac pro and I've had the 2.66Ghz mac pro as well.. pretty much owned everything from 20" ACD, 23" and the 30" and returned the 30" as it had terribly uneven backlighting the right side was clearly brighter than the left side. But kept the 23" and now sold it on ebay because I dont need the external display + I smell new updates coming soon anyway.