Everybody who has a 3Dfx add-on card has to put up with reduced picture quality at high resolutions. At 1280x1024 fonts are often blurred and working with your computer becomes all but a pleasure. What's the reason? First you have to consider the signal quality being primarily responsible for a good picture. The best monitor can only be as good as you expect it if the video card provides a high quality signal. But this signal becomes weaker the more connectors you have within the cable line (e.g. extension cable or 3Dfx loop cable) and also the longer the whole lane is.
This is a reason why e.g. the Matrox Millennium cards are preferred by many people despite their poor 3D quality and performance: Because the signal quality assures a maximum of picture sharpness. Another way to improve the picture quality with expensive monitors is to use the BNC input instead of the standard D-SUB connector. Each of the three color signals (red/green/blue) as well as the two control signals (horizontal/vertical) have their own shielded lines to preserve the signal quality as good as possible.
What many of you may have already done to temper the picture quality problem is to obtain a loop cable of highest possible quality. Usually the brand manufacturers of 3Dfx cards ship their products with decent loop cables by default. The quality of those loop cables can differ very much, thus they actually limit the highest resolution.