I'm using the PEP66 and it blocks one of the four DIMM slots on my Soyo SY-6BA+IV mobo. I don't use a Peltier or anything but I do run Rain 2.0. My PIII 700, which is O/C'ed to 970 MHz, idles at 19C, gets to 22C or 23C surfing, and maxes out at about 33C in Q3 or UT. I occasionally run it at 1011 MHz and the temps are about the same as at 970 MHz.
1.Old Antec Case, Asus PC-DL, 2 x 1.6 LV D1 Xeons @ 3 GHz, 2GB Corsair PC3200 @ 200 MHz, Chaintech 6800 128MB AGP
2. Old Crap Beige Case, Gigabyte GA-H55M-S2H, Core i3 530, 4GB CL8 OCZ DDR3-1600, eVGA GTX465
3. Asus Pundit mATX Case, MSI AMD Zacate E350/dual core E350IS-E45 mini-ITX, 4GB CL9 Crucial Ballistix DDR3-1333, LG Blu Ray/HD DVD & DVD Burner