Help With Upgrade Priorities

Could I get to the link to your motherboard? Only z75 I can find is the Pro3.

Anyway, I personally don't find it worth it to upgrade from a 7950 to a 7970 since it's only 1 tier higher. If you find yourself in need of more frames, what I would do is just add another 7950 on Crossfire.

Whoops, it was a Pro3. Got the two confused looking at other threads with the Extreme version. I'll edit my original post.

Also, wouldn't I be bottlenecked since the other PCI-E slot is a 2.0x16 at x4? Here's what it has according to Newegg:

Expansion Slots
PCI Express 3.0 x16
1
PCI Express 2.0 x16
1 @x4
PCI Express x1
1
PCI Slots
2

Yes, it would bottleneck. I was under the impression there really was a z75 Extreme3, and as far as ASRock motherboard history goes, all Extreme lines have Crossfire support.  

Alright. So a Z77 MoBo (if it's the extreme edition)would give me Crossfire support, but what else is different about it compared to a Z75? Is it a faster chipset, more optimized for overclocking, perhaps more bandwidth? Just wanting to clarify what the difference is between the two boards.

Nothing much, really. Z77 boards usually have more features than the z75 especially on expansion slots, but that's about it. They can both OC.

Alright. I looked it up, and if I bought a ASRock Extreme4 or Extreme6 Z77 MoBo along with another MSI 7950, it would cost about the same. If I got the Extreme4 version, though, I could probably afford more case fans to help cool the crossfire configuration.
The only difference between the two I can see are these:
Extreme6 has a PCIe 2.0x16 at x4 speed, as well as a mini PCIe. It also has a display port and a IEEE 1394 connector on the back. It has a sli/xfire power connecter, but I'm not sure what this is exactly and whether or not you would need it. It also comes with random things like a front usb 3.0 panel, and a rear usb 3.0 bracket as well as some software I don't need. I'm thinking of getting it mainly because it's the same price as the graphics card I planned to buy anyways (when bundled with an identical 7950 to mine) and I like USB 3.0, but would it really be worth the extra $30? I'm not sure what a crossfire power connecter is, so could anyone help me clarify that.

Lastly, is a 620w Silver certified PSU put out enough juice for a 7950 crossfire, or would that be pushing it? (I don't have any extra voltage on my overclocks, they're all at stock volts since I'd rather not mess with anything that can seriously fry my hardware if I mistype or click)
I looked at extreme.outervision.com/psuengine and it seemed to be fine, said the minimum needed would be 580w at peak load for all components, but I'm not sure if I trust this. I've tested my PSU, and it seems to put out all the stated voltages on all of it's rails, so that shouldn't be the issue. Also, how bad would it be for my PSU to push it this hard if I plan to replace it with better within 6 months of the purchase (once I save up some after the MoBo/7950 purchase)?

I believe all the Extreme lines have Crossfire power connectors. It enables you to do 2-way Crossfire - meaning 2 GPUs stacked to achieve a significant boost in performance; in your case, 2 7950s. You don't need to do this outright, you can wait until you find the need to or when you have cash to burn.

500-550w would be more than enough for a single GPU system even at full load. If you want Crossfire in the future as an option, 750w would be best to get.

The calculator was including both cards. I was wondering if my current PSU would be fine for about 6 months of running the system, even though it would be near full PSU load. So the crossfire power connecter is different from a crossfire bridge?