Check your M6's meter against your M6 TTL using a similar exposure scenes that are in question. If they are the same then get a good hand meter and check against that. Also, you should turn off the auto-correct on your scanner and adjust by hand.
I've used some Ilford film and I don't really see any 'weakness' when compared to Kodak
You should be able to read a newspaper writing through the darkest part of the negative. This is an easy development check. But you should tweak your development further if you aren't 100% happy with the results.
There many testing procedures in photo books and the internet. These are really complicated and require a lot of time.
Chris Crawford here on RFF has some great tutorials for your problems: