I have a 2004 996TT cab with 6-speed (w/short shifter) and the X50 power kit. I used to have a 2001 996TT coupe with the standard motor and that generation Tip. The ownership of both overlapped for a few years and I drove them back to back quite a few times.
Here's my take on the subject:
I bought the Tip coupe mainly because I found it quite difficult to properly heel-and-toe shift the manual transmission owing to the inadequate foot-well space provided in the 996 series. I'm 6'4", wear 36" inseam trousers and find that my right leg interferes with the console when I try to heel-and-toe. This immensely limits my enjoyment and proficiency in 6-speed driving. It's quite frustrating.
I found the Tip to be somewhat sluggish in making up its mind to downshift. However, the Tip provided an unmatched continuous flow of power that was very difficult to duplicate with any 6-speed when accelerating onto a freeway. It remains very satisfying to me.
I traded a '99 996 Carrera 2 Cab 6-speed for the 996TT cab. My wife and I shared the former as well as the new car and I asked her which transmission she would prefer. She said she really wanted to shift gears and I knew I wouldn't be taking the cabriolet to the track, so I quickly agreed to the 6-speed.
The X50 engine with 6-speed gearbox is a somewhat unhappy combination for multipurpose use in my Cabriolet. First, there is quite a bit more turbo lag in 1st gear with an X50 power pack. The larger, higher maximum flow rate turbochargers take a bit longer to spool up than the plain vanilla variety on the normal motor. It turns out that the 0-60 time is no better than from the standard motor, when paired with a 6-speed. In order to get the most low-speed action from the motor, pairing the X50 with a Tiptronic is required. This is because the torque converter lets the engine move into a higher RPM range sooner than the 6-speed allows, thereby reducing the apparent turbo lag. Honest
Also, in any kind of steady speed traffic situation, the Tip always seems to know what to do when asked, even if it takes an extra blink of the eye. The 6-speed uncovers a number of somewhat bad manners that the X50 motor has at light loads. There is a slightly dead spot in the very light throttle range that feels kind of cheap for a $150,000 car. It's kind of like backlash in the throttle position. One can lightly increase the gas pedal pressure without much result for a period of time, until the ECU servo thinks about it for a while (during which it seems to
decelerate a bit), and then slightly over reacts. Since the motive power is not buffered by a torque converter, the sensation comes directly through to the seat of ones pants as a surging sensation. This has no effect on max throttle operation, but exists only while trying to smoothly obey the traffic laws. The Tip had no such problems that I can recall.
If I had it to do all over again, I would have ordered the Tip for the Cabriolet TT as well.
This isn't the same situation as you face, but your decision should be even easier because the 997TT Tip gives up much less driving dynamism to the 6-speed than the 996 version did.
And, I actually like having both hands on the wheel while track driving, too.