Yah. My K6-2 450 is rated for 2.2v but needs 2.4v to run stable. It would dump out of certail 3D games for no reason (particularly Descent3). To run at 504Mhz I needed 2.6v and some better cooling (nothing like newer Athlons need, but better than the older Pentium/K6-2 heatsinks were.
Also some boards will let you lock the memory to the AGP bus so it will run at 66Mhz with a 100Mhz system bus. I needed to do this to prevent the infamous blue screen of death. I could run cas2 all day at 75Mhz (112Mhz system bus), but could not run cas3 at 100Mhz for memory and bus.
AMD Phenom II x4 945 3Ghz | ASUS M4A77TD | 2X WD 1TB SATA 2 hard drive | 2x2GB Corsair XMS3 | nVidia GeForce 8800 GTS | ATI TV Wonder Theater Pro 550 | Antec P-160 case | Antec 650w Earth Watts | LG Blu-ray Super Drive | LG DVD RW | Windows 7 Pro