a bit of personal experience, a pal of mine has an S4, both our cars are pretty much identical. we both have remaps and run similar FATS times (5.1 secs). when you compare his logs to mine he runs more boost (17psi agaist my 15psi) but less timing. i'd rather run my map because it gives the same results but stresses the turbos less.
when he went for his timing belt swapping he found the timing a tooth out, seems it was set like this from the factory as this was the first belt change.
sort of highlights the need for optimising the engine rather than just winding the boost up. we should do some more logging now. his, in theory, should be quicker now so it'd be nice to see what improvement setting it up properly has made.