That you're holding a cashier's check should be irrelevant to your flying.
Yes, god forbid the guy is using a plane to get somewhere fast...and even worse the man was on a time table and not just boring holes in the sky.
It always amazes me that people seem to think being in a hurry HAS to be a safety issue. Although needing to be somewhere may increase the risk of somebody rushing through something important, things like cancelling IFR to proceed to a field quickly is totally fine in my book .. I guess I'm saying l don't see what your problem with what he DID was. I do have a problem with what he SAID.
Saying "Im not waiting for this slow guy" on frequency to me is pretty rude to say about a guy practicing approaches...we were all there once and I would not want to be hearing that from someone else while flying...
If I was in the OP's shoes I would have just cancelled IFR when I saw the 172 and proceeded VFR to the airport as fast as possible while maintaining separation, which sound like what he did. I however would have saved the insult on frequency.