I have one with an xw7 eyepiece making it 90 power. I use it for finding deer way up on the mountain and counting horns. It needs a heavy duty tripod to stabilize it. Because of it's size and weight it never goes more than a few feet from the truck. It does what I bought it for and I'm happy with it. Also, at 90 power, mirage is a real issue. Once it warms up a little, it's useless. You could always change to a lower power eyepiece when this happens.
If you are buying it for the power (like I did) I'd also look at the Rogue River Super Scope. Good price relative to the German glass, great optics, and because of the double eyepieces, more comfortable for extended glassing sessions. It's even bigger than the Pentax PF100.
Though I only have the 65mm w/ a couple xw ep's, I love the view so much I'm saving up for the 100mm monster. One of the best aspects of the Pentax is the ability to use a variety of 1.25" ep's. The XW line is regarded by many to be the best. But since you can use any 1.25" ep the choices abound. A couple of good links: Pentax - BirdForum
and here Premium Spotting Scopes in Review: Nikon, Zeiss, Leica, Pentax 80mm, 85mm, 105mm Optics
Plus, when you're at 6mmbr punch in "Spotting scope resolution at 1000". In the blog search area and read about being able to see .308 and 6mm bullet holes at 1000 yrds w/ the Pentax 100. (No kidding!)
Well I'm thinkin I'm gonna drop down to the 80mm's. I want to put two in a bracket and I think the 100mm's are just gonna be to big and heavy for this. I don't mind carrying the weight I am just worried about the weight on the tripod.