So let me see if I get this straight- I can buy a 133 board and with jumper/bios increase the speed to (hopefully) 166X10.5, or buy a 166 board and have it run that speed out of the box? Without un-locking the chip? How does this effect PCI bus speeds (are my cards up to it?)?
Essentially NO (answer on the first question). Most of the motherboards around will not allow you 166 stepping that easy. There are numerous problems that will happen. Some boards are made for overclockers like Epox or Abit but more of them are not. So you have to shop for a proper motherboard. The most likely problem you will have is your PCI bus. Then graphic card (onboard cards just won't do), then the memory (you can use PC2400 or 2700 but PC2100 will most likely have the problems here though quality PC2100 should be able to run 166 but that is exactly where they meet limitation and memory will overheat).
So if you have money to shell to upgrade all the components go ahead. And what for? To be able to use Xp1600 processor? Why not buy Xp1800 or Xp1900 and use your standard components. You need to understand that by doing 166 bus on a 133 motherboard you are forcing all the components do that. Plus all of them will dry your PSU more as well so make sure that is ready as well.
Intel situation is totally different, there are 3 reasons for that. Northwood 1.6A can be overclocked by 900 MHz or even a whole GHz. No AMD CPU can pull such a trick. Second the price difference with Intel CPUs are bigger. Third they are lot easier to cool than AMD CPUs, on average they spend less and have less heat dissipation so the 900 MHz is possible with air cooling. Of course even there you need $30+ cooler.
Running up the motherboard BUS clock to increase AMD CPU speed for 300-400 MHz is not an easy job no matter what this fat brain gboz is talking. The people who did it know that. It will cost you some serious time and money. It is truly ridiculous proposal that you should consider XP 1600 plus perhaps another $100 or more in other expenses so that you can get XP 2000 performance after you pushed all your components to the limit???
Some of the problems you won't see immediately, that will happen later once you use your PC at the limit you thought you have. Like crashes and so on.
If you want to use XP1600 buy KT333 board. Even then you might ask yourself a question what the hell was I buying XP1600 when I could get a better CPU.
By the way Kingmax 256 PC2700 chip will cost you about $80 (consider shipping too), Crucial PC2100 is $50 at Best Buy the last time I checked, PNY with Samsung was $50-$20MIR = $30. That $30-50 for one and $60-100 for two. Not exactly that little, at least not for me. Plus Kingmax is not a proper match for Crucial or Samsung brand and the resellers you'll have to buy Kingmax from are mostly the ones with lousy reseller evaluations.