I rode a couple of the local trails on the CX bike included one that is a ~2.5 mile climb that averages around 7.5%. I think the lower portion is closer to 6% and the upper is closer to 9%. It's a mix of hardpack, loose over hardpack, and light gravel over hardpack.
My 700x35c Schwalbe Sammy Slicks had just enough grip to get me to the top without having to jump off. The rear broke loose a few times, but I was able to save it. Going up was pretty fun!
Coming down...a bit of a joke. It took me 18 mins to do the climb and 15 mins to get down. My hands were cramping up pretty bad by the end. If there was any gravel on the road, the front tire had absolutely no grip and I had it skid out from underneath me a few times (got my foot unclipped in time).
For this type of riding, I was thinking of switching to something like a Schwalbe Racing Ralph or Continental Cyclocross King. Will it make a whole lot of difference or do I need to accept that this one of the tradeoffs of a skinny tire CX bike on the trails?
TL ; DR -- Going up = fun. Coming down = suck.