Sell them and get a lot of GTX 750 Tis...evga sc are my favorite.

What does a 750 ti hash at on N?

Up to 150kH/s

Then isnt it better to get one r9 290 with 450khs for the same price as 3x 750ti-s?

But 150kH/s @65W from the wall...

but it will take up more space than one 290

It's a matter of power costs... Only if you have "free" power - R9 290 is better.