not a sure but I think 1gh gpu-miner also have some hidden donation, at least it works strange - eats to much cpu time and also shows not full speed of GPU
on my GTX 580
1GH: ~950-1000 cpm
PtsGPUz0.2ab: ~900-950cpm
PtsGPUz0.3: ~850-900cpm (after optimizations for 384-bit bus? or more donations? )
PtsGPUz0.2ab [disabled donations]: ~1150-1200cpm