In that case, it's not too bad to rely on the readout from poclbm if you freeze all other variables.  You can surely spare a few minutes for the crunching to stabilize =)

I prefer to use poclbm for this since it seems to be stable, steady and has low rates of stales/corrupts (it doesn't matter if your rate is higher if you end up with stale or corrupted shares).  Make sure to not have anything else running that could affect the GPU usage (even newer browsers use some GPU for instance) while you're testing and set -f to 1 (or 0) to give the GPU priority.