I have a GTX660 2gb and a GTX770 4GB, should I use both or just the 770?

[allofyourmoney]

So I just bought a GTX770 4GB. Awesome, the card is beautiful and I am good to go. I use my computer for gaming (typically Battlefield 4), recording (see gaming), and rendering.
Now if I could use both (with some benefit) I would like to.
First concern: Would running two at once have any benefit, or would the faster GTX770 over shadow the GTX660?

My second concern: Would it put more load on my processor? I know SLI is not an option.
Thirdly: Would it be worth it to use both? I believe I should be able to, I have a 700 watt power supply. It only comes with two pci-e cables that are just enough for the 770. But I have LP4-PCI.E cables, and the minimum power I needed for my rig with a power calculator was 550 watts. Thoughts anyone?

PSU for reference if needed (http://raidmax.com/psu/rx_700ac.html)

 

[Rationale]

Raidmax power supplies tend to be pretty bad. I wouldn't risk it. That one can only output just above 500w in real world use.

 

[allofyourmoney]

Raidmax power supplies tend to be pretty bad. I wouldn't risk it. That one can only output just above 500w in real world use.

What makes them bad? And why do you say only 500w when they advertise around 700w? I'm not trying to contradict, I've only been in PC gaming for about a year. And what is a good if not the best brand?

 

[Rationale]

Raidmax power supplies tend to be pretty bad. I wouldn't risk it. That one can only output just above 500w in real world use.

What makes them bad? And why do you say only 500w when they advertise around 700w? I'm not trying to contradict, I've only been in PC gaming for about a year. And what is a good if not the best brand?

That power supply splits its output between two 12v rails, and each one handles about 250w at a time. On 2 video cards considering the CPU as well, that may not be enough. Raidmax power supplies also usually review badly when tested professionally.

Generally Corsair, Seasonic, XFX, NZXT, Chieftec, EVGA, Antec, and sometimes Rosewill make better power supplies. Seasonic is considered the best, though I haven't observed a significant difference from a high quality Corsair unit to a Seasonic or XFX unit.

Your specific Raidmax PSU has scored pretty well on Newegg, so I'm sure it's fine for one card, but I personally wouldn't risk two.

 

[allofyourmoney]

So even if I use the LP4 to PCIE on a different rail it is not that great? I can assume the answer, (no) due to the low wattage on the other rails but I may as well ask lol.