So after I wrote that it occurred to me that there might be a variable that I didn't take into account. Both of the Noco units (my GB70 and the other guy's GB150) were cold as they were in our trucks outside. It's possible that the roadside assistance dude just picked up the JNC660 from inside storage so it may have been warm. In the future if I anticipate a cold start problem I'll warm my jump pack up before attempting to use it, that might help a bit. Wish I had been more scientific in my approach but I just wanted to get my truck started so I could drive home!