Just a note:
I moved much of my information section on my site from .php pages into wordpress and they seem to be doing ok. This was AFTER I was hit by March 23rd Panda, so this is relative.
I unfortunately redirected on popular page improperly for about a week, and after I corrected the redirect, it still took about a month for traffic to resume to its previous level.
So making sure that all pages are redirected properly - or better yet, using the SAME URL structure as before - Is the best thing.
Just my experience. Your mileage may vary.