Got my pair of 6n3p-ev's and listened for a few days. Here are my quick impressions on them compared to the 5670. First, they seem to work fine, nothing blew up.
The 6n3p-ev's treble seems a bit smoother, slightly less sparkly. The mids sound very similar, can't detect any differences. The bass is not as impactful as the 5670. It actually sounds more neutral. I can live with either of these tubes, but a more ideal tube would be one with the 6n3p-ev's treble and 5670's bass. In the end, I'll probably put the 5670's back. I do prefer a stronger bass.