All a person can do is do their research - I think its important as the more people do the more there is pressure on breeders to screen for the likes of HCM.
I do think that there does have to come a point to where a compromise is made though, sadly in life nothing is perfect but you have to weigh it up and you either take the leap or you dont. There is always risk attached to anything.
The breeders you have spoken about sound lovely and really dedicated, I would rather buy from someone like them then one that churns them out like a production line. I do think having looked into pedigrees myself you will find an element of line breeding crop up quite abit whether it be further back in the generations or more at the forefront - I would question the breeder and ask for the logic behind it. There maybe a reason why they are so comfortable doing that breeding.
I must admit you sound very much like myself - I cross reference everything when it comes to pedigrees, and like elaine said I tick off the names in my peds against the HCM list. There is a great breeder who has helped me work out percentages from my breeding/s to know what colours, patterns etc I may produce - so when a blue popped up in my litter I knew there was a chance of it happening so didnt faint too much
I think its great to be prepared but also there does come a point where you just have to either go for it or step away.