The poll is kinda unclear; I leave my N900 set to 1GHz maximum clock mostly, but that's only the maximum; it spends most of its time on a lower clock or completely idle. Do people really manually set the maximum frequency up and down depending on "heavy multitasking", or are you guys just picking option #3 to represent the behavior of the ondemand governor?

Anyway, IMO the thing to do when overclocking is not necessarily to try a bunch of preset voltage profiles, but to build out from the best known-good profile (and if none of the lv, ulv, xxxxxlv, etc. work, the standard one is known good for 600MHz and lower, right?), scaling one clock step at a time, and finding the voltage required for stability. I'd just kick the speed up at the 600MHz stock voltage, and find where it loses stability, or the max, then kick voltage up/down for stability; from that point, you can estimate from the existing profiles how much to tweak the voltage for nearby speeds.

Once you've got stability for every clock you care about, you can go back for efficiency, stepping through all the lower clocks: lock a frequency, decrease the voltage till it crashes, add 2 for a margin of stability, and repeat. It's much less frustrating going down (and getting one crash when you get there) than going up (and getting repeated crashes until you get there).