I agree w/ O-dog. C4's are an upgrade from CM300's, (still love my Nak's though
) I think the C4's have a great crisp sound to them. I havent heard too many Superlux tapes, but I think they are a great mic for the price. I know you said your playback wasnt the greatest, but still, the decision should be up to your ears. Dont let someone talk you into one mic being better than another w/o checking it for yourself. Plus, if you run Nak's or Superlux, you might not get as many patchers since they will be looking for the German mics.
Jim