If you're aiming to cross the threshold at the same height in each case - say the EU-OPS 50 ft for perf A a/c* - and assuming you follow the slope all the way to the surface:
with a 3 deg gs you'll touch down 50/tan(3deg) ft down the rwy; i.e. aprx 950ft.
with a 5.5 deg gs you'll touch down 50/tan(5.5deg) ft down the strip; i.e. around 520 ft.
Thereafter, your rollout ought to be the same, for a given set of conditions.
Steep approaches iaw EU-OPS can also be certified with screen heights less than 50ft**, gaining you even more in those cases.
*OPS 1.515, for those that are interested.
** App 1 to OPS 1.515(a)(3)
I recognize that the original poster mentioned a positioning flight, so it doesn't require to adhere to the EU-OPS criteria.