My 64 neck, and my CS 63 Strat, are both closest to modern C, compared to a U or 57 V. But they're actually way fatter. Very sneaky. Very, very comfortable. Because I'm familiar with modern C, I tend to compare these to that. But if I think about the timeline, how modern C didn't exist yet, then it's easy to see the transition from the fatter necks. It's an oval C, wider, fatter than a modern C. It melts into my hand, and disappears. As for getting used to different profiles, I play a Martin OM-28V, which is bigger than the U necks. And switch to a thin necked 335 without a thought. You get used to it. That said, these late 50s, early 60s Fender necks are the ones that fit me like a glove.