A couple of thoughts, I'd expect the sound to be length dependant all else being equal, that is length from the back of the inlet valve to the trumpet not too the butterfly.
So short inlet runners on long trumpets or short trumpets on long runners of guess the result would be similar.
That said one is a rubber trumpet and probably absorbs more sound, the trumpet shape probably also has a part to play.
Unless you're going to modify your bonnet it would seem you don't have much choice on length, of you've got to make a new inlet manifold anyway you may as well try the steel trumpets as you have them anyway.
