Interesting discussion so here are my thoughts...
In my view EGT sensors are too slow acting to drive any kind of anti-knock measures like retarding timing or adding fuel or water injection
I don't see anything particularly wrong with running rich apart from the damage it does to your wallet. The 1980's F1 turbo engines employed this strategy during high boost qualy runs and you can see Rod Millens Toyota 503E race engine in his Pikes Peak Celica and Tacoma run rich. It's messy but it works! The only downside is the risk of bore wash. I understand the previous owner of my JDM ST205 lost an engine this way.
The normal 'kit' water injection strategy is pre-emptive triggering using boost pressure so its quite effective at combating the sudden rise in charge temperatures which are a consequence of higher compressor speeds. In practice this translates to the WI only activating during transient phases as you spool up the turbine during accelleration. Whether you'd describe this as 'full time' I'm not sure? Just to be clear I'm not planning on using WI as part of my standard strategy with my Track Toy unless I've grossly overestimated my intercooler capability
It should be more than capable of handling the ACT transients.
Don't Porsche use VNT turbo's? If the VNT units are prone to failure through hight EGT's I'd have thought the forums would be full of horror stories from the porker owners.
I'm not in favour of running road car engines close to det. The marginal increase in power may be worth it in a race car but pretty pointless in a road car where reliability is more important.
The current crop of turbo 1.6 litre World Touring Cars breathe through a 42mm intake restrictor and run 2.5bar absolute (1.5bar above ambient) at a 12.5:1 CR for 306bhp and 247lb-ft. This CR is not untypical of modern turbo engines and is a marked change from 1980's technology where CR's of around 7:1 were quite common in competition engines. This is probably due more to advances in materials science, cooling technology and most of all electronic control systems. Interestingly the Chevrolet Cruze TC1 touring car built by the highly successful RML team employs a Life ECU which is probably one of the most advanced ECU's available today having been developed originally by AER for their Le Mans 24 Hour LMP2 winning 2litre turbo engines.
As this is Mike's project thread I'd better just say that I agree with his approach of over-speccing his build and running the engine significantly below the power it would be ultimately capable of delivering