Not counting GVs (bleh), I've done 8/9/10 in half the planes in the game, probably. From 109s, to 190s, of all versions, to p47s, to n1k2s, to ki84s, to mossies, and so on.
However, the highest I have film footage of is 16 kills in a c205. Numerous 12s, 13s, in C2s as well. In this case a friend landed kills for me in the buffer so I (having just hotpadded and reupped) landed and returned the favor. I seem to recall 18 in a C205, but apparently no film for that one, or screenshot.
I did, however, land 12 kills in a C202 (film proof of me landing). All of them fighters, and only 1 hotpad halfway through (after wasting ammo on a lanc and not getting a kill).
Then again, I have millions of sorties with 1 kill (or no kills) so it all evens out.