I know I'm a little late on this thread, but I have the rb header/presilencer with stock catback. I haven't seen a problem yet. Of course, I don't have cats, but I don't know how much of a difference that makes.

ive seen it done

but i heard it doesnt work out well in the end and ofcourfce doesnt give you the significant power you would get untill you get the whole Exhaust system its self

if its not there for too long i doubt itll do any harm

just dont wait too long though