I have the headwall and used it quite a bit this past season, and did some testing on it before that in a multijacket test reveiw. Do not have the guide pro to help out in that comparison.
I did find the headwall to be good from wind resistance stand point, yet still maintained a great degree of breathability . But when i did a water test on it. It handled a soaking rain(simulated from a water hose at a rate of 8-12 inches per hour) quite well and wetted out in the shoulders at 11 minutes. There were a few small leaked in seams before that which were not detrimental to the overall water resistance. By 15 minutes the entire torso was soaked thru as i sat there. Hood was very comfortable when wet and allowed great visibility. I would suspect this jacket in a very light rain would hold up well for a while until it wet out.
I did review the proximity LT jacket by kuiu but not the guide pro.