Penetrations - Coming To You. I remember it to be pretty impressive.
Aren't you confusing it with the Penetration "Come Into the Open" 7" or "Coming Up for Air" album. Penetration was a 1970s punk band (they reformed though) with lots of metal/progressive influences, listen to "Stone Heroes" or "Future Daze" for metal off the first album. Far from obscure, although there's a lot more punks than metalheads that know about this band.
One band that seems sort of similar is Zorro. Their 7" has 2 punk numbers, then the last song is more like nwobhm, way too much progressive influence to be punk, although they seem to be categorised as nwobhm on the internet, I haven't personally heard any other songs by them to say what kind of band it was. Another funny thing is that everyone posts the back cover for the 7", I've never seen the front.