TTRS setup using the cheaper 340mm TTS discs instead of 362 / 370mm??
That's a good option, and is about 1200 quid from AKS for the full kit, rather than 2 grand for the 362mm 2 piece kit.
Incidentally, I was reading through a thread from a couple of years ago about the 996T 4 pots with 350mm Merc discs. One comment suggested the calipers were a better match to the mk5 master cylinder than TTRS calipers. Although everything I've read about TTRS piston area says they're pretty much perfect and not too large (unlike Porsche 18z 6 pots). Maybe something to do with more 'staggered' piston sizes with the 996T calipers, rather than judging it by total piston area alone.
The 340mm TTS discs are a good thing in themselves though; much lighter than 345mm R32/S3 and the 350mm Merc discs.
I'd stick an R32/S3 caliper on with 340s myself, but the weight of the calipers puts me off.
I can fit 18Z behind my Ultras without needing wheels spacers as with TTRS calipers I'd need spacers. The 350 mm discs are 13 kg while the 340 mm can weight 10,2 kg from Brembo.
Find me someone who has a mk5 Golf with a 23 mm3 MC that has fitted the 18Z and reports problems with the brake pedal. Mine is pretty hard and I step on it with all my strength repeatedly and the pedal keeps firm and high. 
In my country wheels spacers are illegal so it made my choice easy.
The guy with the mk6, quite a recent thread but I can't remember exactly who. Although, that is just one case of anecdotal evidence to my knowledge - anything else has been technical evaluation on paper. So I'm not claiming it as solid fact.
To be fair, you've answered all my questions about brake upgrades on the mk5 platform with sound knowledge, and I respect that knowledge.
I'd imagine some degree of subjectivity comes into this. Much like suspension, where 'one man's hard and crashy is another man's tight and responsive', maybe some drivers prefer a more progressive pedal feel, that other drivers would describe as soggy, or simply much more pedal travel than they're used to.
While you're here, do you know much about the 996T calipers?
