Does your current rear wheel have a cassette or freewheel? http://www.sheldonbrown.com/free-k7.html

If it has a cassette, you don't need a new rear wheel/hub. Just get the chain tensioner of your choice and an SS cassette cog and a spacer kit to fill the gaps. If it has a freewheel, then get a SS thread on freewheel and re-space/dish the wheel as necessary.

IMO, it's not worth getting an ENO hub/BB for any mountain bike. A chain tensioner works just fine and doesn't super ugly like on a "road" bike.

But I vote for option 4: find the magic ratio. That's what I do on my bikes. No tensioner, no expensive wheels, just a little fiddling with gearing until I get the combo I want.