I dont think rushing is a good idea in challenge mode, unless you got a deathwish...

But there's a key to it. The base maps are to be rushed, since there are lots of areas you can evade. Jail1 is NOT to be rushed since enemies attack you from behind, set abushes, etc. The city levels and power stations are to be played without rushes -there's plenty of ammo and health, and monsters too-

But you bypass all the ammo, items and weapons, there's a big price on rushing levels.

I know where all the items are, since I've played quake 2 since it's release. I pick items and rush.