I would suggest you stay away from a 4bar fpr unless you upgrade the fuel pump, it puts a lot of strain on the fuel pump. You are in my opinion much better off getting larger injectors. Cost of a 4bar for and new fuel pump is more than injectors.
Saab red tops are ideal for this turbo, 346cc at 3 bar is easily enough for 270bhp which is more than this can kick out.
With regards the mapping, do you really want a k04 map on a non k04 turbo? It has a completely different compressor and is no way really comparable to the k04. Admittedly £60 is a good price but I can only imagine all they are doing is sticking a k04 map on your car , that's not really tuning it! And the suggestion of a 4 bar fpr is because they've done it before and hence have a map for stock injectors and 4bar.
I appreciate you want to stick with apr as you've got a stage 2 from them but really you need a custom map tuned for your setup and not something which has just been put together on someone's car and being flashed onto yours.
£60 map from apr or custom remap from the likes of r-tech which is going to be better?!