@heat: depends very much on the hash type you are processing. some hashes are running the cards very hot with high power consumption (e.g. wpa). some others are keeping the cards cool with very little power consumption (e.g. bcrypt).
i personally prefer one fast system than 2 separate ones. but the decision is very much depending on what you are actually trying to achieve with it. either one can be the better choice, depending on your needs. so it would help if you can specify what hash type is your main target and what you are trying to do with it. will it be running 24/7 365 ? which hash types? how about allowed noise levels? american or european power supply (110v vs. 240v which would allow a 2000W PSU)? server/rackmount or desktop chassis requirements? as kiara said, more cards in 1 box might need better cooling, heavily depending on hash type though.
i personally prefer one fast system than 2 separate ones. but the decision is very much depending on what you are actually trying to achieve with it. either one can be the better choice, depending on your needs. so it would help if you can specify what hash type is your main target and what you are trying to do with it. will it be running 24/7 365 ? which hash types? how about allowed noise levels? american or european power supply (110v vs. 240v which would allow a 2000W PSU)? server/rackmount or desktop chassis requirements? as kiara said, more cards in 1 box might need better cooling, heavily depending on hash type though.