Mass Effect Mass Effect is set in the year 2183 AD. Thirty-five years prior, humanity discovered a cache of technology built by a technologically advanced but long-extinct race called the Protheans. Studying and adapting this technology, humankind has managed to break free of the solar system and has established numerous colonies and encountered various extraterrestrial species within the Milky Way galaxy. Utilizing alien artifacts known as "Mass Relays", the various space-faring species are able to travel instantly across vast stretches of the galaxy.
This game is based on the Unreal 3 engine but has noticeably higher system requirements, BioWare created very detailed environments making this title quite demanding, you’ll need a high end system to run this game at high resolution with AA enabled:
AA scaling between the two cards is quite similar with this title, they both handle Mass Effect nicely at max detail without AA enabled, going to Vista drops performance by 5% for the X2 while the GTX 280 gets a 9% increase. When enabling 4xAA performance drops 30~40% on both cards under XP, under Vista the hit is slightly smaller but still very noticeable.
Using AA levels higher than 8AA with the X2 is not recommended, the QAA modes of NVIDIA should not be enabled as performance drops below 30fps and gameplay becomes very choppy.
For a detail view of the results, with AA scaling and XP -> Vista Scaling see
this table
...8xAA on ATI should be compared to 8xQAA on nV, not the 8xAA which is 4xMSAA based CSAA mode
...16xAA on ATI effectively turn the card into single chip card which can do 16xMSAA, since both chips render the same frame with different AA patterns
...16xAA on nV is 4xMSAA based CSAA mode and 16xQAA on nV is 8xMSAA based CSAA mode
So 16x and 8x comparisons in your graphs are far from being 'fair' or 'apples-to-apples', the 8xAA should have ATI 8xAA vs nV 8xQAA (8xQAA = 8xMSAA) and 16xAA shouldn't even exist since the GTX280 can't do 16xMSAA which is (practicly) what the HD4870X2 is doing by blending the same frame rendered twice with different AA patterns.