The larger carafe on the BlendTec will make an enormous difference in blending performance, and not only because it has a 4" blade. I've noticed when blending things in the past that a narrow carafe causes larger food items to simply float or bounce around above the blade. A larger base, especially with corners, will allow the food to fall next to the blade, and also help it get stuck, at least momentarily. Giving the blade a chance to cut through it.

Matt, you could always go whole-hog and get one of the commercial BlendTec products with a 3 year warranty. $1200. Zing. Available all the way up to 2400 watts and 20 amps!

I've personally used a Vita-Mix many times and I quite liked them. But if I were to buy something today, it would probably be a BlendTec with the Wildside carafe.

The bottom edge of my upper cabinets is also only about 17" off the counter top (due to a valence), but that wouldn't be a big issue anyway. I'd probably set up a pedestal near the foyer to show off such a blender anyway.