The basic difference between the 12 & the 14 is $$$

 

OK, Tried it today on way home.
Buy One! It does exactly what you are looking for.
First of all, both downshifts and upshifts are faster than the display can change, and there is no silly speed limit to when you can go into 1st (within reason I presume)
Its lighting quick! And yes you can jump from 1st to 3rd as fast as you pull the lever.

You must know some good roads where you will put all this to use. One note, while there is no lag whatsoever, the throttle is cut ever so slightly so as to remain civil to your clutches and self- but you wont notice it other than the lack of the thump.

 

I tried it on the way home in my 07 XKR tonight and don't notice any delay at all. The gears change immediately with each pull of the flappy paddle. I don't know if it makes any difference but I do have the GT3 TCM tune on my car though.

 

I tried it last night, and did not notice the delay. I'm not sure where I go the idea.

I did three rapid clicks, it went from 6th to 3rd quite rapidly at 50MPH, about as fast as the engine could rev up the difference.

My impression with the XK's gearbox, is that it is quite acceptable for an automatic. It surprised me on the test drive. I'd been only owning manuals from my first car onward.