I spent a few hours both yesterday and today with the Flea 47 and the Mercury.
Yesterday we used the V72s and today the V76m.
The V72's is thicker and darker than the V76m similar to increasing the proximity effect.
The mids are solid and the top end is restrained while still remaining clear.
I would describe the tone as creamy, rich, velvety etc.
The V76m not only has more gain than the V72 but they are sonically a little different.
In comparison the V76m, though not quite as weighty, is by no means lacking in low end.
The V76m also allows a little more of the high end to come through.
Using something like a Pultec I think either could be made to sound close to the other with some small EQ tweeks.
The V76m is the obvious choice for ribbons for both the extra gain and also the slightly more open, less thick tone.
With the 47 running into the Mercury there's now a definite 1950's sonic vibe happening!