At stock boost pressure 0.8bar and slight over boost spike say, 1 bar the UK 550 cc injector are safely within its limits of injector duty of 80/85% which equate to 440bhp.
This for me at stock boost and budget single turbo kit works very well for a UK Auto Supra with FULL BPU supporting mods. Plus there is no stress to engine and gearbox.
Naturally i have test this set up on our Dyno and AFR's are not LEAN at stock boost.
So at that level of boost in mind i don't see no reason to spend/waste more money on bigger injector, fuel controller, boost controller, extra labour costs and remap fees.
For someone who wants more power, say max border line 550bp on stock auto then they have the latter option.
So as far as i'm concerned this Supra is the finished job.