An EF12 sounds pretty good, IMO.. close to a vF14 at half voltage on the filament but the VF14 has a a different texture to it, not necessarily better but different
I'll preface this by saying yes--I am fully aware of all the internet squabbling about how an EF14 is, sonically, not the same as a VF14; it seems to me like this discussion becomes more 'pie in the sky' every day due to the lack of availability of VF14's.
I have a pair of U-47 'tribute' mics where they were built the same way by the same guy a couple of months apart--the intention was to build a fairly matched pair. After the topic someone (Max?) started a couple of years ago about EF14 vs EF12, I had the mic maker switch one mic to an EF12. It changed the character of the mic enough that I elected to leave the EF12 in because it became another useful 'flavor' in my toolkit. When compared to the EF14 mic, the EF12 mic's character is less aggressive/forceful, less 'barrel-chested', more open & feels less dark than the EF14 version. The EF12 mic gets at least as much use on vocals as the EF14 one... maybe more. Sonically, it kind of sits midway between the EF14 mic and my (prototype) ELA-M250 'tribute' mic.
I feel like getting a good-sounding tube is KEY to, particularly, having good-sounding large diaphragm tube mics for use on vocals. In my somewhat limited experience, every tube has its own signature, although I found 5 Star GE 6072's to fall into a couple of families sonically. If someone could come up with a way to substitute an accurately-performing replacements of excellent examples of the 'unobtanium' tubes it could be a GREAT thing for the microphone world. I'm interested to hear more about these products.