PII's had the mulitplier limited ,in otherwords you couldn't exceed the def 3.5x but you could set it lower.This is useful on a BX chipset boards (or latter chipsets)
I used to have a PII233 @ 280 MHz (2.5x112) ,it also ran at 293MHz (3.5x83).
I have heard of a few reaching about 330MHz
Timers
Your 1st question ,yes!

2nd your board needs to have selectable bus speeds (via the bios ,jumpers or dipswitches) & also preferably selectable multipliers if on a BX chipset(or latter)
3rd about 290-330MHz (depending upon cooling)(they run damn hot btw!:Q)
4th Yes! ,isn't free speed always worth it?

5th Buy a new 1 if you can afford it & if overclocking it doesn't make it fast enough for the games he plays