Jnosol

Please excuse the newbie here. There are 4 reasons why one would want 19" over 20":
1. More tire options
2. Wider treads
3. Lower operating cost (cost per tire is less than 20")
4. Less unsprung weight

What OP is proposing only checks off #4. Custom tires will cost more, it's not wider, and limited to one option.
Honestly, I think R888 265/35/19 front and 325/30/19 rear would be the best option. You can drive R888 to the track and drive the same setup home. It's easy to find, not expensive, and it gives you loads of grip.

Raising and lowering the car isn't hard, just count the threads and shouldn't require alignment if the changes are only 10mm w/o touching other suspension components.

Fitment should be around 19x9.5 ET50 front and 19x12 ET46 rear. You'll need camber front and rear. Need to replace the lower control arm bolts with the slimmer Panamera style bolts, otherwise your wheel barrels will be scraped during load. *another way is turning the bolts around and grind down the side would be touching the wheel barrel (Thanks Jamie at Dundon).

Mvez

You guys are overthinking it, and obviously have never run 305 Nittos. They are big. I ran 305-35-18 Nittos on 12" wheels for years, as does almost every 997 driver, and it is not "stretched". The RE71R is still a true street tire and they don't run as wide as NT01, that's why it looks streteched.

Does this 305 Nitto on a 12" rim look stretched to you? It's not. That's my old car. The 19" would be the same. That 305 looks no different than the 325 Trofeo mounted on my current BBS wheels (1st pic). Look at the 245, it's big and almost bulging on a 9" wheel. That's how big they ALL run.

I'll say it again. This size will better fit all 991 cars, including those running 11-12" wheels, allow for less extreme camber requirements, or 9.5" front wheels. It makes the best business case. You can ask for whatever size you want, but my suggestion is based on actual facts and tire use mounted on rims, not website data. There are already plenty of 265/325 tires out there, we need at least ONE set of tires that match stock sizes in 19".

If you ask for a 325-35-19 or a 315-35-19 you actually increase the rolling diameter, if you ask for 315-30 or 325-30 you decrease diameter, neither of which we want, we just want to match the CURRENT rolling diamters, so that we can run the car on the street without lowering. Not to mention, once you start lowering cars too much, you get into all kinds of bumpsteer and geomeotry issues. Correct size tires allow for ideal ride heights with stock components.

If you can't understand why we need this size, then this thread probably isn't for you. Pretty simple.

Jnosol

Makes sense now. I submitted the NT01 size request.