I am 80 kg an have a rebel 8 and rpm 10. Too much overlap. At 60kg I think a 6 and 9 would be sweet. The 10 is my main kite on a tt in Perth so a 9 will get 60kgs out in 15 plus knots
6,8 & 9 are the sweetest sizes. The 10 comes with 23m lines and is more for unhooked tricks rather than pure freestyle. I had an 8 and 10m, I dont have the 10 any more. Any C shaped kite over 10m just doesnt have the balls out performance that you want from such a kite. They do such sweet kiteloops.
As the others say, Its a factor of "Average Winds" in your area and your weight.
but 6 and 9 sounds good if your in Melbourne Victoria which averages 16-25 in summer.
Ps I have ridden nothing but a 10.5m (i'm 68kg) for 2 seasons. Definitley need smaller kites in W.A. I am just about to buy an 8m in able do surf (with bigger boards) and more advanced/unhooked tricks.