I respectfully disagree with mmadmikes1. I use a "brew bucket" which will hold about 7G to the rim as a primary for my wine kits and I've never had any problem with it. If you were buying something either way I'd say get the 8G but if you already have a 7G it should work just fine and you can use the money you saved to buy more bottles or some fancy labels or something.
Also- FWIW- My wife and I just bottled that kit not too long ago. It makes a pretty decent finished product. A little sweet for my taste but I'm not a big wine cooler drinker. My wife (who likes wine coolers) loves it.
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-= I believe I'll have another beer. =-