No, I did only use the released build from the official homepage. Why is there no link to access the test builds on the homepage of ioquake3? The link I just got from this forum got me there, but without that link I would have no idea of how to get the test builds.
I recently downloaded a modification on top of ioquake3 that adds proper widescreen support; in other words 16:9 aspect ratio without all the weapons barely visible beneath the HUD (in vanilla Quake 3/ioquake3, only half the weapon is visible when selecting widescreen). The modification goes under the name "IoQuake3Arena 4K" on moddb, but it seems that this mod is also based on the very old release build of ioquake3, thereby having the same slowdowns.
The test build however fixes the slowdowns, but I suppose the console command for "lifting" the weapon upwards in the console is still listed as a cheat, as in the main Quake 3 Arena game (and all the games using the Quake 3 engine)? I'm talking about the commands such as cg_gunx, cg_guny, cg_gunz.