Nothing that you should be worried about. There are plenty of high powered C1's out there with no issues what so ever. All OEM Honda cranks are excellent.
b18c6 is heavier due to slightly different counterweights, both can be fitted to the same engine as they are same stroke with same size journals on both the main's and rod.
I know this is an old thread but i got a crank the other day in a B18C block and it has C4 stamped on it but it also has the R stamped on it. Can anyone help?