Why such honking great big heatsinks? Just go with the standard OCZ version with normal heatspreaders, but get the 1600 instead of 1333. Then you have less headroom to make it to that higher clock. Plus the difference in price shouldn't be that great.
If you are really set on using them then my advice would be to go on gigabyte's website and see if they have a schematic type drawing of the board with measurements. you'd be suprised, I have found this sorta stuff on a number of different hardware manufacturer's sites before.
Ok, in all seriousmess, with your system specs, four gig of 1600 RAM will be fine. I wouldn't fuss too much about having more (you can check out on OCZ's webpage a comparison of how more RAM affects gaming performance, and anything over 4gb is minimal). As for the 'overkill' heatspreaders, there is a reason why 'normal' heatspreaders are the norm... it's because thats all the average user will need. I gave the advice of getting 1600 with normal heatspreaders instead of 1333 with big heatsinks because I assumed you wanted to overclock to 1600. If that isn't an issue, then I guess you could even go with normal 1333 modules, but personally I think the small price difference warrants stepping up to 1600.
Give these a go: http://www.newegg.com/Product/Product.aspx?Item=N82E168...