Unfortunately, no one here on Head-Fi has been able to review the NE-8s and NE-7Ms head to head. So it's really been a toss-up in terms of which to buy.
As an NE-8 owner, I can tell you that the music produced from them sound excellent. I only say that they are a bit bass anemic probably because I'm comparing the NE-8s to my $400 IEMs such as my TF10s and W3s (kindof unfair). All in all though, the NE-8s sound great, the soundstage is good, details are good, and the bass is very clean.
I think that your decision to get the NE-7M or the NE-8 comes down to your personal preference. Do you want something with a bit fuller bass? Go with the NE-7M. NE-8s supposedly have greater detailed mids and treble, so maybe you'll prefer that. If I were you, I would just 1) flip a coin. Or 2) get the NE-7M. It has a built in microphone and it's about $8 cheaper

Can't really go wrong with saving some money.