A long-time good senior player. Heck what's Jack Nicklaus' handicap these days? Arnie might be a 15-handicap five-key player. There are going to be outliers - that's all I'm sayin'. :)
Yeah, the sample sizes for those were pretty small. Dave will tell you that when he has Key 5 he will shoot 66, and when he doesn't he'll shoot 71 to 75.
Best without? 19. Best with just one? 11.
Do you mean Key #1 or "the first key" (which is often Key #1)? The first key is the easiest yes, but at the same time once you get Key #1, Key #2 gets easier for some and more difficult for others (ask Zeph), but once you have Keys #1 and #2, Key #3 often falls into place more easily than either #1 or #2. Some also have an easy time with #4, but then get hung up on #5 for the rest of their lives.