... As you can see, I'm missing quite a large range between 85 and 175.
This is where I can see big advantage in the popular 50-500mm "Bigma"
If you haven't decide yet - take a look at the Minolta 7D (it could be had for the price of an XT after rebate), couple this dSLR to the above Bigma and you'll have a fantastic combination including an 'antishake' system that will work with all lenses
, all the way to f/1.4 with some primes: http://www.steves-digicams.com/smp/07102005.html
Heck at that price (less than the cost of 1
IS lens) it could even become handy as an 'IS only
' 2nd camera... :-)