Derek,
It doesn't sound a lot, the difference between 1.5" and 2".... until you do a little bit of maths
Imagine you chopped a slice out of each size of wand, to look at the cross-section:
The area of a 1.5" diameter circle is 56% of the area of a 2" diameter circle.
However, the circumference of the smaller circle is 75% of the circumference of the bigger one.
In plain English, what this means is that bigger you go, the lower the ratio of tube wall to air. This causes less drag on the air moving through the bigger tube, thus making it perform more efficiently in the airflow department.
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OK lets look at another plain English example.
Imagine you buy a car and drive it for the first 100 miles with the handbrake slightly on. As soon as you realise and take the handbrake off, what's going to happen? "Wow it goes so much quicker".
When used with a high performance machine (i.e. not most portables), increasing your wand bore size does exactly the same as taking the handbrake off, it reduces a restriction in performance.
Once you get your head out from up your bum and fit that glide to your wand (
), you'll also realise that before the glide, 50% of the time you weren't recovering much up the wand and back to the truck