The D610 with a 50mm f/1.8G lens is on sale for $896.95. The usual cost of this lens is over $200. Not a bad price to move into FX if the D750 is out...
I found this PDF for a Tamron 24-70mm lens (not sure if it is the same model lens as the one you have). According to this, you might be looking for a...
PLEASE READ: Due to an error on my part, I deleted the first poll and started over. So even if you voted before, you need to vote again. My apologies...