AVG has been a solid product for a very long time, but they really sc***ed up everyone with a 64-bit machine this past week with an update. Thankfully I changed to Avast about a year ago. I was getting ready to go back to AVG but after this week I will not do that as I have a 64-bit machine.

There isn't any problem with running multiple versions of Office on a Windows machine, can't speak for Macs. Just be aware that if you decide to uninstall one of them then it might cause issues with the other - or not - I've seen both outcomes. Many of the people I know at work have both versions of Excel for the very same reason you mention.