Sounds about right for the V35 and thin neg at 5x7. My negs are fairly dense and I usually end up around 12s at f8 with the 5x7s. I've lowered the voltage on the V35 by using the 250V setting (although we have 230/40V here), that helped a bit. Check your voltage setting if there's any room to go up a notch. Going to 220V with a 120V mains might make it way to dark. However, another pragmatic approach would be using a transformer 120V->220V then setting 250 on the V35.

Are you using the color module? If not try to get one. Those filters also swallow some light. Using ND filters under the lens is another possibility.

Cheers,
Andi