would loading entities on the fly help, see umans script for that, plus having triggers for enemies.
also I found having any lighting on enemies made frames drop like mad (good job I changed the word mad from the hebrew word for the Greek Tartarus, I wouldnt want a mod pretending 'again' I was swearing on the forums), no dynamic lighting and you can have a whole bunch of them right in front of you, stick dynamic lighting on, so the models of the characters are lit and bamm it went down to nothing.
Basically my overview is , fpsc is a very very bad engine, just made really bad, probably the worst running engine, but what it can do is build games very very fast due to having the painting segments, its also great with the moving up a level and how it ghosts the other levels, keeps the spatial awareness down having that which is a blessing, and the fact that you have media packs, if it didnt have these 2 things it would be a pile of, * space here for words of your choosing*. But the speed of painting segments and the packs is a time saver, so if you are in a hurry, a game with problems is better than a game that isnt made, get a quick game out, do what you can and move on to something else, so its a time saver really, but not much else in my opinion
Butterfingers is doing a traps pack, so one can perhaps get rid of the entities problem by making a game filled with traps instead, then just having a couple of enemies in it now and again.
I think that once they have released dx10 at retail and ported code over from dx10, if it stll has problems then just offer out the source to see if anyone else can fix it, perhaps move onto a new product making a 2d version of fpsc, ie a 'click and play' 2d game engine should be there next direction, that would be a teriffic program to have it it worked well. Other 2d engines that are supposed to be click and play are not really, well yes and no, TGC are very good at making things very simple, Im sure they could make a simple interface for a product like that for non coders to use, that is as long as it worked.