38 to Onyx Summit is part of the Breathless Agony ride a few of us did last May. BigBear is another 10 miles down from OS. Section you mention is from mile 47 on of the profile! I think the roads are actually nice compared to the opposite direction to Big Bear (hwy330?). The climb is popular among the cyclists so most of the vehicular traffic is aware that there are cyclists on the road.
Same weekend is Matteo's Baldy Challenge. Some will start from the bottom of Baldy/GMR. There should be atleast 15 to accompany you if you attend. From The base should be a similar ride to the rt you mention. Drive from Berdoo should be about 45 minutes. Worth it to meet the SoCal people!
