Wow I never heard of Kirby before. It looks like a good vacuum. I found a good review of it on:
http://www.epinions.com/content_62335389316
According to this author, you are a sucker if you paid more than $900 for a G6.
When I was doing research on vacuum a year ago, I came across some bad reviews of Dyson vacuum, including the review on Consumer Reports. I ended up choosing a Hoover upright for $200-300, based on its recommendation. I'm still happy with it.
Couple of recomendations:
Get one with disposable vacuum bags. I thought those bagless vacuums were great, but it's disgusting to clean them out, and those filter replacements are quite expensive.
Rotating brush will loosen the hair on the carpet easily. If you have hard floor or delicate carpet, get a vacuum where you can turn the brush off.
Get a vacuum with motorized wheel.
These 3 are pretty common features, but somehow I had hard time locating one with all these 3 features in one machine. I really really hate bagless vacuums. I threw 2 out before settling on the one I have now.