Finally after some searching found data ("Max Boost by C.Bell") where turbo lag was plotted vs engine rpm for both small and large turbos. These numbers give our tts max acceleration in a very short 4500-6600 rpm range if driver wants minimal lag.
...................._____________lag (sec)_____________________
...RPM .....................small turbo ...............large turbo
...2000.........................0.6............... ...........0.9
...3000........................ 0.5......................... 0.85
...4000........................ 0.3......................... 0.65
...4500........................ 0.25....................... 0.5
...5000........................ 0.18....................... 0.42
...6000........................ 0.05........................0.18

Has been a real experience getting max acceleration from my tt (without limiter shutting engine down) after driving nonturbo M3s for last 10 yrs. Finally realizing importance of high rpm to instantly utilize tt's full power.