It's been a while since I saw V4, but you can transfer parameters across parts by ticking the check box next to the parameter in the parameter window and then deriving the part with the parameters you need into another part. Just don't import any of the geometry or surfaces unless you want them too.
I still don't have V7 yet (waiting on IT to install, but it includes a large number of features not included in V4. Weldements, decals, text embossing and engraving etc just to name a few. V6 ran slower than 5.3 for most people (myself included) and from what I hear on the newsgroup V7 has addressed many of the slow down issues. I don't think V7 has any new features over V6 and the files are interchangable between those two versions.
Hope this helps.
Steve