would a good set of Pioneer or Kenwood 2 way 280W speakers equal the sound and performance of Premium rear parcel shelf speakers, or would they even be better than?????

Any average branded 2 way speaker will be better than the stock. So either Pioneer, Kenwood, JBL, etc will be better. This is assuming you are talking about the parcel shelf speakers.

If you want to upgrade your front speakers, I'd suggest going with a split system where there are separate tweeters. You can get lower ranged types which can run off the head unit and don't come with a separate cross over box, simplifying the process. However you do need to install the tweeters in a new location. In saying that, you can also just upgrade the 6" speakers in the doors for better mid range. I can't remember if the stock tweeters are good or not sorry.