64 bit version tests:

my results.. for 680


C:\Users\gateway\Desktop\rpcminer-mod-x64\bin>rpcminer-mod-cuda.exe -url=btcguild.com:8332 -user=xxx -password=xxx -gpugrid=2048 -gputhreads=256 -gpu=0
Client will start 1 miner threads
Work will be refreshed every 4000 ms
1 GPU GUDA device(s) found
CUDA initialized
Search Configuration for gpu named: GeForce GTX 680
Your device:
   - 8 streaming multiprocessors (SM)
   - can run sm version 300
   - bitcoin miner is optimized for 5 gpugrids per SM
   - max value for gpugrid parameter is 2147483647
max nonce 3FFFFFFF
Done allocating CUDA resources for (2048,256)
iterations on gpu=32 blocks=2048 threads=256
Iterations: 63,hashs per iteration 16777216
Target = 00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffff

Here is what im seeing..

}
119645 khash/s
118523 khash/s
119082 khash/s
119110 khash/s
Found nonce 2A7B43AC
2013-04-08 19:32:46 Found Hash!