you linked a 6850, not a 6870.. and the 6870 is like $60-70 more, of course its better.
The Halo Don
A GTX 460 1GB should be the same price as a GTX 550, and its stronger, a lot stronger.
I recall EVGA has a lifetime warranty, so I'd pick that. MSI is more high quality in general but the warranty is only 3 years in US so practically you should choose an EVGA videocard if you want it to live forever. Unless you upgrade every 3 years then I'd suggest MSI because its more reliable quality anyway.
oops , i listed a 6850, but its better than 550ti and is equal to a gtx 460.