The gigabyte one (first) is actually a 1GB 4850. AND, its stock overclocked, and looks like it has a much better cooler on it. the sapphire is 512MB, not as big a cooler (essential for 4850 i heard it gets a little hotter than other cards) but $20 less. personally i'd go for the gigabyte.
@Giedrius
It would run, but you would definitely definitely have it on really low settings.
The sapphire is also 1GB..
The gigabyte cooler is actually aluminum but painted to look copper. It's also a Zalman, a company which makes good coolers.