Need a perfect 8mm hole - to ream or bore?

[miopicman]

That's what engineering is. i.e. whatever is adequate for the purpose. There are pros and cons for all methods.

I have a similar engineering situation and I will be using an undersize drill followed by a reamer. The pros for this is that it is quick and can be used over and over again with consistant results. Like a twist drill the reamer can be used more than once. Also a reamer will make a consistantly parallel hole; this is something to be aware of when boring deep/long holes - is the lathe quality good enough? You don't want to end up with a hole that is ok at one end and tight or slack at the other.

This my part. It's a chopper disc for speed feedback on a spindle motor.