seanlo:

I've read often about how Poser doesn't work well with triangles, but I have to say that in my experience it just isn't true.  I've converted conforming clothes to .obj's and deliberately "split" the rectangles into triangles to get a smoother look.  Also, there are dynamic clothes--made as dynamic clothes--consisting entirely of triangles that work like a charm and run very fast in simulation.  So I would say to ignore the warnings and try it yourself.

Regarding the slowness of converted dynamic clothes in simulation, I have the same problem.  I don't think there is much you can do about it.  One thing you can try is to run the drapping simulation only, then export the drapped object, and try running the cloth simulation over that.