You've been spending a lot of time agonizing over a case, but since you're not OCing, you're going to do fine with cooling (and I've OCd everything from a Pentium 166 to a 3200+ in all types of cases) in just about any of the new cases you're looking at. You have the right size in mind for your new rig. Pick 1 with the features you want, door/no door, window/side blowhole, drive rails, front panel ports, etc. You'll find those things more important, imho, as a new builder. As far as quality, when you pay more you'll get better materials, rounded/rolled edges inside, more features, etc. Pick one you like looking at, 'cause that's what you'll be doing for a long time!
Noise can be a major issue, but unless you want silent or near silent, spend some money on GOOD FANS and speed controls. The cheapo fans that come with most inexpensive cases add a ton of noise to the machine - and they're the ones that are right on the outside, buzzing away all the time. You'll use the stock HSF, and the regular chipset fan on the mobo and video card fan will make some noise, but you're not going to be too unhappy since this is your 1st build. Add the fewest number possible of good, speed-controlled fans to keep the inside of the case cool.
Finally, think about ditching the floppy drive for a combo card reader/floppy (I think Mitsumi makes one).
Happy building!