You know, I'm seeing a pattern of Phenom users with 1066MHz memory complaining of stability problems when they're overclocking. It might not be what's holding you back, though, since you're not touching the memory divider or the FSB, right?
First question, though, is: do you have ACC enabled? You MUST have it enabled to break 2.9GHz using the multiplier. Also, make sure the TLB patch is set to disabled - if it's on (and it doesn't need to be on for a B3 Phenom, since it has no TLB flaw) it'll slow down your computer by anywhere from 5-15% or so.
Assuming you do have ACC enabled and you're still having this problem being stuck at only 2.9GHz, my first thought is that you might not be feeding your ram enough voltage. DDR2-1066 ram generally needs more juice than DDR2-800. If you've got the ram voltage set to default, it might only be giving you 1.7-1.9volts when your ram might want 2.1volts, for example. Try going for 3.0GHz again (set the CPU multiplier to 15) but don't adjust anything else, and try setting your ram up one voltage notch at a time until you get to 2.1volts. If you still aren't getting anywhere, then it's not the ram voltage that's holding you back.
If that doesn't work, one hunch I have is that you could try moving the North Bridge voltage up a tad just to see if that brings some added stability.
Finally, once you've got your memory voltages set correctly, and your 9850BE is purring along at 3.0GHz without any additional CPU voltage (mine didn't need any for 3.0GHz), you can you can give the Phenom core more volts and start taxing the limits of your cooling. The AMD stock HSF is a decent heat pipe design, and I'm running at 3GHz with it right now, but it is not the best cooler you can use for the 9850BE. You'll have to make that decision if you want to get a 100-300 extra MHz out of your cpu for the starting price of ~$50-~$100 and up you can spend for a better air cooling solution. Check out this site for cooler comparisions:
http://www.frostytech.com/
By the way, folks on that site are talking about a "brand new, never before seen heatsink straight from Korea which is going to give the Top 5 coolers a run for their money," here:
http://www.frostytech.com/permalink.cfm?NewsID=71382
so I'd wait to read what the heck that solution is and how much it costs before you spend money on an aftermarket HSF.