revo stage 2+ K03 cars consistently hit 280bhp and about 320Ibft torque providing they have all the supporting mods available. I think they could now surpass by a few more bhp with the new ITG and twintake once people start to use them more often.
add to that some water meth injection and added mapping I reckon 290Bhp is achievable
to achieve this you would need
uprated DV
uprated fuel pump,
bigger intercooler,
turbo back exhaust,
neuspeed turbo discharge pipe
a very good air intake
Water meth Injection
and a map that can utilise the benefits of water meth.
maybe even a PCV fix and a good sevice to ensure then engine is running at its optimum
290bhp 320Ibft should be achievable then, but i think 300bhp is a no go zone, unless you start bolting on nitrous kits