How to undervolt/underclock 290x for mining?

[dankknightavngr]

Is it worth to pick up a 290x blower style for $100? And how do I make it run cooler and consumer less power?

 

[dankknightavngr]

If not, which of these is a better deal:

Gtx 970 - $150
r9 390x Trix (no backplate) - $150
gtx 1060 3gb - $180
gtx 980 - $200
Rx 470 - $200
rx 480 4-8gb - $220-240
gtx 1060 6gb - $230