Andrew Buck :
Looks like the PSU might be overloading. Not really by any means a really good PSU, not even 80+ rated. Go for a good XFX one. Also make sure that your system is stable.
Decided to take your suggestion and go with the XFX PRO750W Core Edition. Should be arriving Tuesday or Wednesday. Will update on how it goes. I'm aware it's way over the requirements for a single 7870..but I like to future proof and am considering a new motherboard and running a crossfired setup maybe sometime later this year.
If the system still reboots I'll likely bite the bullet and go for a 7950 as replacement (and overclock it as much as possible), buying another 7870 at this point just doesn't seem worth it. Anything higher end is a little out of my price range. When looking for an upgrade to that I intend crossfire 7950s (with a new motherboard) which, should be sufficient for a while.
Thanks alot for your time.