I came close to trying a walmart drive, but wound up using newegg on a 320gb HDD for 79 bucks..and had it the day after I ordered. Plus its the 16mb cache and 7200 rpm...so I stepped up from the stock Ps3 drive. I dont see a huge difference in the times for booting, etc, but I dont hear the drive either, and I dont see where the HDD is going to make that much of a temp difference.
i got the scorpio black 320. I considered a 500gb, but thought logically about actually using that much room on my Ps3..when I rarely use 200gb on my Toshiba laptop - and I love this thing. So I used a little restraint and only allowed myself the 320gb.