I'm using 25 meters of VGA lead from computer to projector at church. Bought the cheapest as I wasn't sure that it would work at all, but quality seems indistinguishable from the case when I use same kit with a 1 metre lead. With one exception: there is a small amount of cross-talk from the 'deaf loop' circuitry which runs in the same cable path. (although the VGA cable doesn't go all round the loop, obviously.)
If it were that important, I would get one of they 40 quid shielded cables with gold plated pins at each end, and run the cable on another route... but it doesn't seem important for what we need.