you can take a hot air block just as fast as a 109 block.
deck height is different. but only a matter of thousanths.
as mentioned above, the valley webbing is viisably differant. the hot ai/na blocks have a more "porous" valley casting, while the 109s are a more definetive cast.
I have not ever seen any proof of the pre-109s being weaker than the 109s.