Pretty sure there is no limit.
On the
multiplier, there is. It's limited to 5, so the maximum amount of perks you can get for a single kill is currently 40/2*5*1.25 = 125 perk points (killing a B-29 in something like a Spit I and landing it at multiplier 5.0)
That being said, my own max number of perks I ever landed was 98 or 99. Single sortie, no rearms in a C.205. But it was many years ago when the C.205 still had an ENY of 40... (planes like Spit I had ENY 60 back then)