You are right. Sli is useless for mining. Hence why we use 750Ti's which can not do sli.
Not the only reason but i had to mention it

ooo and for anyone interested, i just boosted my MSI GTX 750Ti's to 1.4GHz and their running stable mining groestl.
Right now the increase from 1.3GHz to 1.4GHz and made a large improvement from
3.1MH/s to 3.4MH/s, all with an increased power load of 2W!

so to state, each of my cards now consumes 2w more power, however produces almost 300khash/s more. So a 9% improvement for a 2% power increase. And the shares being submitted seem to be more stable aswell. If it gives stability issues i will be sure to let you all know. Performance with the new groestl release when its out will be very interesting. i wonder if overclocks will keep.

Thats a question actually, have you noticed an increase/decrease in TDP under the un-released groestl code? As if you havent, overclocks should remain good, and if you see triple performance, my overclock could get triple benefit (0.9MH/s) on each card