Higher kv vs. taller gearing

I killed the 7xl in my yusa buggy when I geared it up to do some speed runs, the rotor separated from the shaft. I had been wanting a lower kv motor for it anyway. I plan to buy another feigao for it (because I cant afford a neu right now), and Im wondering how much lower on the kv I should go. Im thinking I should do a 9xl geared 18/52, but I could also do a 10xl geared 20/52 and get almost the same speed. Im wondering which setup would run cooler/ be more efficient, or if there would be a difference. Any opinions would be helpful.