Hi Graman, it’s relatively easy to calculate which GPC you need. You need clear sky with Moon, a ruler and a piece of paper. Here on pages 9-10 there’s a good explanation how to do that:
https://www.baader-planetarium.com/e...l_12_pager.pdf
I’m Sydney North Shore based. I don’t have 1.25x GPC, but got 1.7x and 2.6x ones.