Oh I didn't mean run it and remove it later; I meant run it on a week-long server beta (or shorter if it's obviously a problem) with intent to wipe it at the end of that time and use those results to inform whether thaumcraft can be included.
OPIS profiling during that time with a few users would show pretty quickly what percentage of our TPS thaumcraft is eating (just by existing). Assuming TPS will always decline from the 'ideal' conditions that a freshly generated world offers, thaumcraft eating more than its share at the start warrants cutting it from the release
The particular problems causing inordinate lag were Angry Zombies and trees in the Magical Forest biome.