Well... looking at those numbers, I would call those far more reasonable and expected than your prior example. They are pretty much in the normal range and it is expected that the size will tick up and then drop back when the garbage collector fires.
That said... nUI does not interact with any of Bliz's menus and windows such as quest log, inventory, vendors, quest givers, etc. If you're seeing issues there then there's some external variable that's impacting your game engine.
Have you ever done a clean install as per the instructions in this FAQ?
http://www.wowinterface.com/forums/s...ad.php?t=21716
If not -- I would highly recommend giving that a go and see if it resolves the frame-freeze issue you're having.