As for the Puma, I fear you're likely right. ENY of 25 or less just has that unplesant feel of truth to it.
Well I'm kind of torn on it, Puma will be a fast scout car I think 53mph with an 60mm L/60 gun on it - It does have a secondary MG42 - far different then the MG34 most tanks have, kind of curious how this will be modeled.
But as a scout car (as it was intended for recon) it did come with 6 Smoke launchers, I think it would be a quite interesting to see in game.
My view is that the M-18 has a better hitting gun, and 50 cal anti aircraft gun and a Tank Destroyer, Puma is a recon car (strictly it was forbidden to engage tanks) - however in Aces high I can see it as being a fast reaction vehicle.
One reason I put the ENY higher then M-18, is fact it doesn't have a 50 cal anti aircraft gun, it would be defenseless against aircraft's - armor wise its close to an M18 - 30mm in front and 10mm on side/rear.
So you are gambling on higher ENY and no AAA - vs Lower ENY - better gun and AAA.