The EN7900GS Top is for the first time faster than the senior model from ASUS, but not by much. The game engine probably doesn’t load all the pixel processors and TMUs, so the lack of them is easily made up for by the core frequency.
Both graphics cards have a considerable advantage over the Radeon X1950 Pro and are somewhat slower than the Radeon X1900 XT, not counting in the results of the overclocked EN7950GT. If you enable FSAA, the EN7900GS Top and EN7950GT provide a comfortable frame rate in 1280x1024.
Serious Sam 2
The engine of this game, on the contrary, makes full use of all of GPU resources. Using shaders with multiple texture lookups, it is sensitive to the amount of TMUs. The game is also sensitive to the amount of graphics memory: graphics cards with 512MB of memory have much higher speeds than models with 256MB.
The large gap between the ASUS EN7950GT and the EN7900GS Top looks natural then. The former can be used to play the game with enabled FSAA at least in 1280x1024, but the latter cannot yield even 45fps on average. The cards from ASUS have similar minimum speeds, though.