As far as rumours go, word on the street is that Asus will be the only manufacturer using the 512-core GF100's in their upcoming Fermi Matrix. The reasons might be the huge heatload, but also the inferior overclocking capabilities. We all remember how the GTX275 Lightning overclocked so well that it passed all other GTX200 series cards out there in, for instance, 3DMark Vantage: link. I am quite confident that both GIGABYTE and MSI are using the less high-end Fermi chips for this exact reason!
NVIDIA seems to have overcome initial hiccups with the GF100 graphics processor, and could release a new graphics card that makes use of all 512 CUDA cores, and 64 TMUs on the GPU. The GeForce GTX 480 was initially released as a top SKU based on the GF100, with 480 out of the 512 CUDA cores enabled. What NVIDIA calls the new SKU is subject to some speculation. While GPU-Z screenshots show that the 512 core model has the same device ID (hence the same name, GeForce GTX 480), leading us to believe that this is a specifications update for the same SKU à la GeForce GTX 260 (216 SP), it seems possible that the release-grade models could carry a different device ID and name.
Expreview carried out a couple of tests on the 512 core "GTX 480" graphics card, and compared it to the 480 core model that's out in the market. NVIDIA GeForce 258.96 drivers were used. The 512 core card got a GPU Score of 10,072 points compared to 9,521 points of the 480 core card, in 3DMark Vantage Extreme preset. The additional TMUs showed an evident impact on the texture fillrate, 41.55 GTexel/s for the 512 core card against 38.82 GTexel/s for the 480 core card.
In the second test, Crysis Warhead, with Enthusiast preset, 1920 x 1080 px, and 8x AA, the 512 core card churned out a framerate of 34.72 fps, while the 480 core card trailed at 32.96 fps. In this short bench, the 512 core laden GF100 card is 5~6% faster than the GeForce GTX 480. If NVIDIA manages to release the SKU at the same price-point as the GTX 480 as it did with the GTX 260-216, it will increase NVIDIA's competitiveness further against AMD's ATI Radeon HD 5970, which is still the fastest graphics SKU in the market. Below are screenshot comparing scores of both cards.