do you really want people to spec out an entire build for you... at least pick out the case - thats the most personalized part! not to mention... $800 - 900... for an i5-2500k build... difficult... but i'll try.
So it's about $950 with shipping - and the mobo leaves you room to eventually go crossfire and you can upgrade to an SSD when you feel necessary. You can get rid of the h50 cooler to go to a cheaper cooler or no cooler at all.
pluses - 2500k, 8GB ram, 5850, and h50 if you ever decide to try overclocking.
cons - platter drive (non-ssd)
Without the h50 it's under 900 with shipping, and if you aren't overclocking you really don't need it. but I would still recommend something.
I'm sure other people will come with other builds though this is just my suggestion.
it would affect your startup times by alot. 20 - 45 sec startup. but it wont affect your games (you'd install everything over 100mb to your 1tb drive). also, from that 60gb you'll have abt 45gb usable (after windows install).
its not really necessary. i only put it there if you want to reach 800. maybe it can be something you can get on your next pc, when prices come down.