Crossfire upgrade question

Hey, so i am currently running a asus hd 4850 reference board from when the 4850's just came out. I love the card, but I'm thinking of upgrading a little bit. Considering I have the capability to Crossfire, I thought that would be the most cost effective way to boost my gaming performance. I was on newegg and contemplating 4850 cards and I'm not sure whether to go with a 512mb (like the one I have now) or get a 1 gb.

The two cards I am considering are:
HIS HD 4850 512MB IceQ4 - $99.99 (- $20 mail in rebate)
[url=http://www.newegg.com/Product/Product.aspx?Item=N82E16814161244][/url]

SAPPHIRE HD 4850 1GB - $124.99
[url=http://www.newegg.com/Product/Product.aspx?Item=N82E16814102837][/url]

I like the bigger cooler on the HIS and how dirt cheap it is, but i like how the SAPPHIRE has more ram.
I guess the question is, is the extra ram worth $45 and a lesser cooler?

Thanks for the help!

^That is correct. The 1 gig card will only be able to use 512 meg of memory.
What you want ideally is another of the EXACT same card you have, to minimize the chances of a problem of the 2 working together. This is not supposed to be an issue, they should all work no worries, but I have seem some people have difficulties running different brands.