Frogger,

Experimenting is always good. If you have some alternative use for the corrugated drain pipe if your project DOES NOT work, then you lose very little if your "experiment" fails.

If you went PVC to the crest of your hill, plus maybe a little farther, then there would not be that much pressure on your transition connection - if the rest of the pipe run was truly flat or slightly downhill.

I would figure out that connection first. If you think you have a chance of it working, then try your hybrid system. If that doesn't work, just finish it off with PVC the whole way - and then you only "wasted" some inexpensive corrugated pipe and a few connections.