I've picked up a few planes here and there. I've got a 6" Stanley block plane which is my main inquiry. The bevel on the blade is 25 degrees. I got it from a family member and it seems fairly old. This afternoon I went to Focus (the UKs equivalent to Home Depot) and looked at a new blade. It states on the back of the box that the main edge is 25 degrees and the remaining millimeter should be 30 degrees. I would assume this would apply to most blades but I don't see a specific reason for it. Would this reduce the amount of chatter while planing?

I've noticed differences between my smoothing plane the block planes and my spokeshave by as much as 5 degrees. Would it make sense to alter the edge say to 20 degrees?

Cheers