I've found image quality is highly reliant on what type of monitor you use. If you have an old 17"/19" CRT, using Quality/HQ won't make much difference since the picture quality sucks anyway and with a 17" AF makes very little difference (tested this with my 17" iiyama and 19" diamondtron crt). If you have a decent modern monitor then there's a fairly sizeable difference between Quality/HQ using the nVidia card if you use AF. With Quality AF you will see shimmering in some games that won't be there as much if you use HQ filtering.