who knows how fast exactly the blitz collision system is - but it's probably faster than a recursive entitydistance check. For one thing, blitz probably splits everything up into sectors etc. even if the sectors aren't the most intelligently placed. it probably also handles speed better than using entitydistance. Plus most likely it's written in optimized c or ASM. Their might be ellipsoid-elipsoid dlls available, and with a little effort I could right a not-so-great one.