All consumerish cards are single-link. That's enough for 1600x1200, even 1920x1200 via so-called "reduced blanking period" timing.
HOWEVER, as a number of articles has demonstrated, the DVI transmitter integrated into the NVidia range of graphics chips has a signal quality issue that limits it further down. Thus, unless your particular card uses a discrete transmitter chip, your mileage may vary. You might be able to do those 1680x1050 at reduced frame rate, or maybe not at all.