The more I think about it, the more I want to try my GPS.
I have used it in heavy woods on tight singletrack on my mountain bike. It was as accurate as my friends computer as far as the speeds. The tracking was VERY accurate.
I have also used it in VERY heavy, thick, up and down twisty slow and fast woods on my motorcycle. Once again, did fine in comparison to my friends enduro computer. Don't know about the tracking as it was out first time mapping it.
My unit is a Garmin 60csx.