|"my RAM is set to 166 MHz"|
The RAM is supposed to run at the same frequency as the CPU (1:1 ratio). You're actually losing performance with the ratio at 133:166 (4:5) . Change the RAM speed to 133MHz.
Chances are the CPU multiplier is locked. Some of the early AXP 1800+ were unlocked but the vast majority are locked.
"the 1.49 Ghz I've got, I've Oced to 1.6 Ghz"
What's a 1.49GHz? AMD didn't make any CPUs that run at that speed. It's either 1.47GHz (1700+) or 1.53GHz (1800+). If you got it up to 1.6GHz at 139MHz frequency, that means the multi is 11.5x, so it's an 1800+. If you had the RAM set at 166MHz, that could be the reason why you couldn't go any higher. However, you MUST lock the PCI at 33MHz, AGP at 66MHz. If that's not possible, they will overclock along with the CPU. Take it too far & you risk corrupting the data on your hard drive, having problems iwth the sound, video, or anything else that runs on the PCI/AGP bus.
We need the make/model of the board.