Okay I believe you, I just wanted to point it out. I will try some testing the Sqrt vs. InvSqrt, just to check the difference. Not in DB, just in general. But it is up to you, Numsgil, to decide if an error rate of 8 % can be accepted!? You are the one with insight in the formula etc., and therefore you are the one who should know if it makes a big impact on the simulation.
Now Quake 2 and DB are two entirely different computer programs, and in DB it could make a lot of difference if a algorithme is very dependent on the Sqrt, and thus making large differences in the sim. Just like the butterfly-effect, just a tiny whiny change can in the long run, have HUGE effects on the outcome. (I consider you intelligent enough to know what the butterfly-effect is... ;) )