Nice, thanks dude but still doesn't explain too much. The shouldn't be so much variance between two similar rounds, that's why we mine in a pool remember?
Here is what I am thinking.( for what its worth) . if you watch our pool hash rate its jumping up and down quite a bit, so even if your numbers are constant you have others with some large miners maybe jumping on at the tail end of a block which then throws all others that have been mining from the start of the block off. I jumped off the pool a couple of times yesterday just so I could see how this works and to see what to expect from another pool as I have done all my mining here on slush only. Yesterday on 19093 my shares was only 2078 as I was only on that block for about the last hour but received just a small amount below of what is normal for me (.0064 vs .0072) which in a small way throws off everyone else that was there for the whole 5 hours. Now what if I was a 500GH/s mini rig doing the same thing...instead of my 5GH/s