The question is do you need the raw power. SLI can have a lot of issues (like heat, noise, game incompatibility, micro-stuttering), but it offers unparalleled performance for the price.
I've heard of the horror stories online off sli/crossfire,but people who seem to use sli/crossfire online never seem to complain,so I don't think it's that bad. I remember you said you have a big power supply so that shouldn't be an issue,just if the cards get very hot like your old one lol