Well there are some things in slush method that I couldn't find described anywhere and I figure them out or someone told me on IRC.
One if a worker goes offline for more then 30 minuts don't turn it on agen till end of a block. If you do restart it it will reset scores for all the workers. I don't get why we have this one. So I just start it with a diffident username from the working worker or put it on a backup PPS pool till the end of a block...
If you have a slow miner(CPU) it can affect your payouts dramaticly(probably because it didn't send any results in for 30 minutes). And never in a good way from my experiences(OK it could be also good but so small that I didn't notice)... I get more since I stop CPU mining with separate worker... I just add a CPU on a GPU worker and it is fine...(I know waist of electricity but I don't pay it per KWh).
So this is just my 2 cents in help for new users...
So what you are saying is - it is better to have 1 fast worker then fast worker and a slow worker? Hmm... maybe that explains how my return varies from block to block for up to 30% even though I do not turn off my workers and their speed doesn't change. Under current algorithm it seem to be better to assign slower workers to some PPS pool

PS. I like Slush's pool but the return does vary significantly from block to block under seemingly the same conditions from my side.