Never tried the 18x20. I'd like to and still consider getting one sometimes for the same reason as you...just to satisfy my curiosity. I would be a bit irked if I found out I liked it better, since I have 3 of the 16x19. Ignorance is bliss.
If I do decide to try an 18x20 in the foreseeable future, there's a pretty good chance it will be this one. It is kinda interesting that all of the heavier TFights (300 g or more) are either 16x19 or 18x19 except for the Ltd. I think it may be the only 18x20 they make. I wonder, does one extra cross really make much difference?
I also wonder if any of the smaller, well-established manufacturers will release any 'spin' frames in the future? By smaller, I mean not one of the Big 5 (Babolat, Dunlop, HEAD, Prince, Wilson). All of those have done so. Will Tecnifibre, Yones, ProKennex, Volkl, or Pacific ever follow suit? Yonex has actually gone in the opposite direction with their recent 16x21 offerings. I'd likely have to try a Tecnifibre TSpin.