Warren in Lancaster, PA
I have sharpened plane irons and chisels at 30 degrees at least since 1975. Full flat bevel. I do not have trouble with chipping, even with harder woods. I think the 45 and 47.5 degree planes were designed around a 30 degree bevel. A 40 degree plane and 30 degree bevel theoretically gives clearance, but more clearance is needed so a sloppy craftsman who sharpens well above 30 degrees will stay out of trouble.
About 30 years ago I was got the impression from reading that a slightly higher bevel was favorable for mortise chisels. I tried to increase the angle gradually, so as to keep a flat bevel, but was not able to get it over 31 degrees. I am back to 30.
I watched a video Rob Millard posted of his sharpening. He said he sharpened at 30 degrees, but in the video I thought it looked a lot more like 40 degrees. He must have gotten the same impression from looking at the video himself, because the next day he reported that his tool was really 39 degrees. Larry Williams video claims about 30 degrees, then he raises the tool "one or two degrees". But it is really raised more like eight degrees and is also around 40. Paul Sellers claims about 30 degrees, also appears to be 40 or more.