I've often thought about buying the 12x10 SEF but haven't taken the plunge yet. I really haven't touched my 6x10 in a long time, it pretty much stays on my MXT which I let people use when they want to detect and don't have a detector. The only two coils that I ever use on my V3i are the D2 and the 4x6. I've had really good luck even in the semi trashy areas with my D2 and if its really trashy I'll put my 4x6 on and that thing is like a scalpel in the trash.
I've read some fantastic results about the SEF coils on the V3i though, there's one person in particular that's very seasoned with the V3i and he said the SEF is much better for the EMI and pretty much close to the same in depth as the D2, he also said that it's lighter than the D2 also, these two perks about the SEF alone is enough to make me want one even more, if my D2 ever takes a dive I'll definitely try the SEF cause I've read nothing but good on the newer nulled ones.