Obviously it depends on the individual chip you get, but the likelihood of reaching 133 with an 800 is better than with any of the faster chips. I am running my 900 at 1.08 with a 120 Mhz front side bus and it is stable with factory heatsink and fan. One of these days, I will have to pick up a better cooler and see if I can get it any higher with stability. I could not get it to post at 133 @ 1.85 volts and I did not want to try it any higher with stock cooling. I am still very happy with it at 1.08 for the $45 + $7 shipping it cost me.
I got a celly 850 too. It's running at 1133MHz/1.85V with no problem, stock sink and fan, temp is about 50C idle. I ran the sandra CPU benchmark, drystone beats P4 1.5G!(What's going on with P4?). The mobo is ASUS P3B-F. Memory benchmark is kinda low, 300+ range. Unfortunately this mobo(and a couple other asus boards) has a bug affecting photoshop users. see: http://18.104.22.168/11040101.htm