PS. Just to help you make your mind, check this link:

http://snapsort.com/compare/Nikon-D5100-vs-Nikon_D7000

I have been using Nikon for maybe 20years, started with their compacs and progressed to a d70 DSLR ,up through the range to my latest D800.
The advice you have received regarding the d7000 is spot on to my mind, you already have some Nikon glass which is a bonus, as regards your desire for a lens with VR and f2.8 it's understandable but with the enhanced AF and the brilliant ISO abilities of the D7000 plus a little work on techniquecancels the need for VR and saves you money.
Over the years I have built up a stable of lenses that suit my purpose and only one has VR the 70-200 the rest, 14-24 f2.8, 28-70 f2.8, 105 f2.8 and the 300 f4 plus a PC1.7 covers all my needs.(by the way I bought them all fairly new but used).
Go for it you will be well happy.

Double post sorry for that.