Tested again with the fan manually set at 80% and managed to complete 3dmark06 with 824/1251. Almost got 12000: http://3dmark.com/3dm06/16386367
Anyway, even with the fan at 100% and memory at stock clocks, with the GPU at 837 I can't even complete the first test. Retried with high AGP voltage and the situation didn't improve.
So, with appropriate cooling, 824/1251 is doable with stock voltages.