I'm going with the 38t chainring as I think it will be suitable gearing wise, but I will swap it for a larger one at some point if the 38t is not sufficient, as some of you predict.

My worries is regarding the 4700 road front derailers ability to shift the chain between smaller chainrings than it was intended to, but since I all ready have the 4700 I guess I'll just try it out, and then get the cx70 if the 4700 doesnt work.