Outlook and Outlook Express are two entirely different products, and behave differently when Messenger is involved. Further, you need a special build of Messenger that is NOT available on the main messenger.msn.com page in order for integration with Outlook to work. It is available at MS's Exchange downloads page.
so if i uninstall version 4.7 and risk experiencing the outlook slowdowns and all other side effects, and do a fresh install of 5.0 it'll still not work 100%?
Correct. Some features will even specifically say "Sorry bud, you need the latest Windows Messenger installed to use this feature" and you will NOT use that feature until you install it. It doesn't need to be running, it simply needs to be installed. There is also code in Windows Messenger that detects MSN Messenger is installed, and as a result, it will automatically set itself to no longer auto-launch at boot...giving MSN Messenger that privilege.
I've uninstalled 4.7, and I have NO slowdowns with Outlook, OE, or anything
Most people don't. Unfortunately, millions of people DO experience slowdowns, not with Outlook, but with Outlook Express and Hotmail (note: there are over 80 million Messenger users at this time). This is why I simply post a warning in many threads that you MAY experience pain if you nuke it.