Mate I have never paddle the Burton but I have a Millenium and didn't think it was that tippy until I paddled a friends Mako 6. The difference is incredible and the 6 doesn't seem any slower.
Don't know if this helps but if you are in the market for one hold out for a Mako 6!
I paddle a Burton Ultimate Wedge (racing version of the wedge) and now a Fenn mako 6. Burton's tippy, probably due to the old design used. The Mako 6 is surprisingly stable even with the 14 and 17 inch width. Get the mako 6 : ) Btw, its also the fastest in the market now.
