two questions about overclocking 295gtx in quad sli

hey guys, im new here, just wondering if you can help me out.

i currently am running two 295gtx's in quad sli and have a couple of questions regarding overclocking. Are my overclocks going to be lower then if i had just one card due to the heat caused my having the cards in sli?

Do all the Gpu's have to be the same clock speed? or do all 4 have to have the same mem, clock ect speed?

this is my first overclock with sli, never mind quad sli..so i dont really want to mess with it without knowing exactly what im doing. i was successful with older cards overclocking but dont want to ruin these cards for no reason, especially since they scream now even at stock levels..

thanks in advance..