Limp mode activity will be mainly based on ECU programming, a stock say 150hp 1.8t setup will never make it to 22psi or so for a number of reasons. This engine boosts in the 9psi area and limp mode restricts it to a 5psi max, When software is upgraded and boost is increased, usually the limp mode level gets increase as well.
I haven't seen limp mode with my car in quite some time but when I did I was running an 18psi setup and limp mode limited the engine to 10psi.
With a K04 you begin to lose efficiency beyond 18psi and as 25PSi stated, it ends up blowing a lot of hot air and it's life can possibly be shortened. On the other hand a larger turbo like a T3/super-60 or T3/T4 hybrid etc. is efficient at much higher boost levels but they are capable of producing more power at the same boost level.
The reason for this is because pressure is only part of the equation, if you want to generate real engine power without risking burning up a too small turbo in the process then what you should really be looking for is increased air flow/volume capacity and a colder more dense air charge (larger turbo and FMIC).
What makes horse power is cold air (dense charge) and lots of it (a turbo capable of flowing large amounts of air at lower pressure levels), a larger turbo boosting lower pressure levels is able to flow as much or more air as a smaller turbo boosting higher pressure levels BECAUSE PRESSURE IS NOT FLOW OR VOLUME, unlike the high boosting smaller turbo, the lower boosting larger turbo is adding less heat to the air charge.
The point is that you want to stay within the efficiency range of your turbo and anyother part for that matter, remove any flow restrictions from the system and keep the charge as
cold/dense with as much air volume as possible. If this doesn't give you the power you want then it's time to install a larger turbo charger, by running 20 + psi on a K04 (not to mention a K03 or K03S), you are just blowing super hot air into the intake and shortening the life of your turbo.
This is no different than those people who think that by turning the sensitivity levels all the way up on a car amplifier or jacking up the EQ sliders all the way they can increase power output beyond the amplifier's rated specs., NOT.
A balance of air volume, cold/dense air charge, boost, fuel and timing is the best way to achieve higher hp & tq levels without giving up drivability, dependability or longevity.
It isn't cheap to do it right, it isn't cheap to do it wrong (you usually just end up paying later).
There is an old saying: "You've got to pay the piper if you want to hear the band".
