6/10 is a gap that works best with a few boards. Im often on my 6 when others are on 7 and 8m kites, but im usually on my bigger surfboard. Its been a great small kite for me but I will consider going to a 10/7 for my next quiver depending on what kite. If I stick with the razor I’d keep the 6 and just turn over my 10. Once its windy and wavy its nice to be on a smaller kite, but most of my riding is strapless.
On just my twintip the gap is still doable, but Im using boots so can hold a fair bit of power. I rig down somewhere in the high 20’s (knots) on that board, and somewhere in the lower 20’s on the surfboards.
OT but 20 knots is kinda this magic number where just above that you can ride almost anything. Ive seen guys holding 12’s down in the mid 20’s boosting large and long when my 6 is also working just fine to tow me around the waves! All depends on how you want to ride. For me with two surfboards and a wakeboard it works great and is dead simple. Kind of a no brainer when deciding what to rig!