SLI - mixing and matching clock speeds/vendors

[imrazor]

I have an MSI GTX 670 2GB "Power Edition" that is factory overclocked. It benchmarks nearly as well as a stock 680, so I'm pretty happy with it. However, I recently got the Witcher 3, and can only run it on High settings, so I'm looking to upgrade. The most cost effective solution seems to be to go SLI, rather than getting a GTX 970. Which brings me to my question...

I know I have to get a 670. But do I have to get exactly the same model and clock speed? My particular card is hard to find and pricier than stock clocked 670s on eBay. Can I just pair my OC card with a bog standard GTX 670 by another vendor?

 

[ubercake]

Doesn't have to have the same clock speed, but has to be the same GPU (e.g. GTX 670) and have the same memory size (e.g. 2GB GDDR).

You can pair your 670 with the "bog standard".

Also, make sure your motherboard supports SLI (usually bundled with the SLI bridge) and PSU can support the second card.

 

[imrazor]

Motherboard is an Asus P8Z77-V LK, which can supposedly support Tri-SLI. Though from the PCIe settings, I kind of doubt it has the bandwidth for three cards. However, two should definitely be doable. PSU is a Corsair 750TX. The only thing I seem to be missing is an SLI bridge. Are they expensive?

 

[ubercake]

Here are the newegg selections:
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&Description=sli+bridge&N=-1&isNodeId=1

The $5-$10 bridge is as effective as the $30 bridge but they don't look as cool.