I'll go for the 27" then, also because it allows for the highest clock speed option (3.4Ghz i7).
The 250GB storage on the SSD really isn't a problem. My current 250GB HDD is sitting at 160GB available. I clean up my computer often enough, don't install anything I don't need and being an MMO gamer there's really only one game installed at a time.
I also have a 500GB backup disk, so I'm not too fussed about removing something from the main disk because I can always get it back later.
It's more the price I'm worried about, but if I'm to upgrade my computer in 5-6 years from now again and I'll sell the one I'm buying now second-hand, I doubt I'll get any decent money from it if it doesn't have an SSD.