I would say it is more like a Mercedes vs a Cadillac.
cannot help on the Q9, but the 8820 vs the 8310 (att network?) size and camera are the two main differences. I am on sprint which is cdma, so the corresponding models are 8830 and 8330.
You should check out the Smartphone Experts Round Robin for a great comparision on different devices, it doesnt review the Moto Q but it covers the windows mobile Os, and it does put the Blackberry on a perspective of non BB fans.
You can try going to http://www.cnet.com , they are good in testing and reviewing the latest cellphones/smartphones plus you can do side by side comparisons. I visit cnet at least once a week. Hope this helps!!