[moredial]

It is more likely that the PR4 site will drop to a PR2 - joking aside, redirects is one thing that Google just never gets right. The other search engines are not much better. Even a year after I had redirects from old to new urls, I removed the redirects and my error logs are full of requests for the old urls - most sent by the search engines.

The best option is to optimise both sites - aim each one at a different market segment so that they complement each other.

In the short term, just stuff the one with keywords - aka as spamming - and hard link to the other. If you use CSS you can get some great artistic effects with this (I once found a M$oft tutorial for using CSS c. 1996 to make graphics using this same CSS / text spamming method).