I have a Nikon D80 w/ the 18-135 kit lens,70-300VR, Sigma 10-20mm wide lens, and 50mm f1.8 (and I love it), and the SB800. I take a lot of low light shots w/ no flash (Concerts, dancers, indoor sports, in addition to landscape photos) so I realized after all this that I needed to upgrade my lenses. Even w/ the VR, in really low to no light and bumping up the ISO, I still can't get shots without some motion blur. I am strictly a hobbyist, so I can't afford the $1600 70-200VR f2.8 (although it's been on my wish list for a while). Someone on another board recommends I get this lens. $$$$$$

I am debating getting the 85mm f1.8 and the Tamron 17-50 f2.8. Or, I may get the 85mm f1.8 and the Tamron 28-75 f2.8. (I'm concerned about the crop factor w/ getting a 28-75mm lens -- any comments from users on this? How much difference does the 17-28mm make? How far will I have to step back to get a shot if I got the 28-75mm vs the 17-50mm?)

I also looked at the new Tamron 70-200 f2.8 at Amazon and am interested in that. My debate with this lens would be, should I get that lens, or get the older Nikon 80-200mm f2.8 for a couple hundred more? I am concerned as to whether or not a lack of VR will be an issue for me. I do have a tripod and monopod, but don't want to have to lug it everywhere I go. In fact, that's partly why I know I need faster glass, because my low light, handheld shots are not cutting the mustard.
A few questions:
1. One more thing, are any of the lenses above compatible wih full frame DSLRs? I'm thinking for the future; I wouldn't want to buy a lens that wouldn't be compatible with cameras of the future. Kind of a waste of money...
2. Does anyone have a list of lenses that are compatible with current DSLRs and usable for full frame cameras?
3. I am concerned that the 50mm/1.8 was not close enough at times and the 85mm/1.8 will bring me too close to the subject on stage in certain situations. Are there any other Nikon Primes people can recommend. Again, my dilemma is to buy the Tamron + 85mm/1.8 for now or buy a few fast primes in different focal lengths.
4.What do you all recommend?
5. Is there a huge difference in the 85/1.8 vs. 85/1.4 lens as far as speed and sharpness?

In hindsight (always 20/20), I realize I should have just bought the body and the best 3rd party f2.8 lenses that I could afford, but being so new to DSLRs I didn't know what to look for and decided to take the 'safe' route by going with the Nikon entry level zoom lenses. These lenses are just not fast enough for the type of photography that I do. Any ideas or opinions?