In terms of gaming performance, the 66MHz memory bus does hinder the Celeron's performance by a noticeable amount since memory performance is a major issue (for example, notice the performance discrepancies between the VIA and Intel BX platforms in the tests). Regardless, the CPU performs respectably for its cost, while it's not a die-hard gamer's solution it doesn't perform too horribly either.
For BX users, you're probably better off with a different CPU, but once again, if you have no 100MHz FSB support, this sort of performance is a blessing.
While the rest of the CPUs manage to max out the TNT2 Ultra, the Celeron 533 just barely makes it. If you're going to be playing at this high of a resolution in Quake III and expect higher frame rates, then you need to consider a video card upgrade.
A GeForce based card would definitely help level out performance as it would offload the transforming and lighting calculations onto its GPU. With a DDR GeForce, getting around 60 fps with a Celeron 533 at 1024 x 768 x 32 can be a reality.