How to georeference a map in UTM / WGS 84 (geographic) to WGS84 / UTM?

I have scanned UTM WGS 84 toposheets, with a geographic grid. I want to georeference them in WGS 84 / UTM (therefore with UTM coordinates). Should I:

1. Calculate the UTM coordinates from the geographic coordinates and enter them for the GCPs, or


2. Enter the geographic coordinates for the GCPs and then reproject in UTM?

I think "1" is cumbersome but more logical as there is no back and forth change from planar to geographic projection.