Please don't, everyone and their dog has access to overwatch now and if watching falsely accused noobs that manage to hit 1 head shot the entire game then get reported is your thing, then have fun.
Also "Neither looked like cheaters to me, or certainly neither were totally obvious cheating". Literally most people are tards (not saying you are) when it comes to OW, all you are there for is looking for OBVIOUS cheats, not well hidden ones etc. If they aren't OBVIOUSLY cheating it's an easy verdict. If you think suspect they "might" be cheating it's not good enough, it's evidence beyond reasonable doubt (aka any doubt).
I rarely report but every now and again I know they are cheating I report and usually a few weeks later I get a Someone you reported has been banned.
I'm not on about one off shots though I'm talking repeatedly waiting angles you don't hold to prefire a player who you can not hear.
Out gamed is the term many spring to but there is only so many times you can say yeah that was luck

i would love to know if i've ended up on overwatch haha