Car looks great in that colour. I do not like the Monza exhaust, it is just wrong to have 4 small exhaust pipes which never seem to sit straight in two big cut outs meant for two large exhaust pipes. It is such an after thought. The original exhaust looks good, and the BTB turbo back not only looks great and makes more power as Monza is just a back box.
The compression ratio is exactly the same on all variants including the Trofeo race cars which put out 200bhp+ using the larger but still small Garrett turbo. I rebuilt the head on one that saw about 10,000rpm after a fluffed gear change at Brands, and all parts like head gasket valves wtc were all standard OEM.
Turbo Technics and Andy Dawson have produced a bolt on hybrid turbo, and in his development car it is running 250bhp and similar torque.