You will also have to change to dual channel memory as the Sandy Bridge memory controller only supports single and dual channel, not triple. Which means going up to 16GB.
Corsair Vengeance LP 16GB (4x4GB) DDR3 1600MHz CAS9 1.5V CML16GX3M4A1600C9 $90 http://www.newegg.com/Product/Product.aspx?Item=N82E168...
I'm using the older TX750 in my Z68 build and it works perfectly fine for what I need it to do.
I'm not the biggest fan of Rosewill PSUs - maybe go with the Antec Earthwatts as they're manufactured by Seasonic.
Yes but you probably bought it when the TXV2 series wasn't available. There is no reason to pay more for the older TX series, not only compared to the TXV2 series, but also compared to other units from other brands/manufacturers.
The Rosewill Capstone series uses a very high quality Super Flower Golden Green design. It has been used in many high quality units.
The only one I can recall which was disappointing is the Kingwin Lazer Gold 1000W and that is because it used some CapXon caps. The caps in all other Golden Greens that I've seen/can remember have been Nippon Chemi-cons, including the Capstone 750W. So build quality is amongst the best you can get below ~$100/150. Performance wise Golden Green based units, according to JG, have an average of just over 1% voltage regulation. Ripple and noise suppression is usually very well controlled; less than half the spec on full load. The Capstone 750W was an exception because it was only half the spec on full load. So again it is at least matching the competition below ~$100/150. Efficiency is also very good, I think against units +/- $5 either side you're only going to have one or two other units which are Gold rated. And not all of those units are going to match the Capstones in other aspects of performance.
Maybe you have read the recent reviews on the Kingwin Lazer Platinum 1000W? If you have then you should probably know that it is a rebadged Super Flower Golden King 1000W, which isn't too radical of a redesign over the Golden Green platform.
There is no reason that I'm aware of not to be a fan of the Capstones; the only reason to choose another unit is needing or wanting a modular unit.
BTW, the Antec Earthwatts Green units which I assume you are refering to are manufactured by Delta Electronics.