want to get more power out of my engine, just wanted to know whats the best upgrade bits to go 4 next, turbo, injectors, etc etc

engine spec as follows

200 Block
7.8-1 Comp
Group A Mahle Piston with Valve cuts out
Wrc high pressure oil pump
Shot pinned con rods
Lighten $ balanced crank
Group A Ported and polished head with inlet and exhaust manifolds to match
Isky double valve springs
Piper BD14 inlet cam + BD14 Exhaust cam
Piper blue vernier pulleys
W.R.C muti layer head gasket
Motorsport Light blue injectors, 3 bar map sensor
Stg 3 T34 turbo with .63 exhaust housing (oil cooled)
Collins polished - 31 actuator
421 BHP & 400 ft lbs @ 24 psi
RS 500 turbo damper
Grp a ramair cone filter
909 motorsport leads
Mocal oil cooler
Full samco boost, water and ancillary hoses (blue)
Radtec rs 500 intercooler
Radtec alloy radiator
RS 500 turbo damper
Grp a ramair cone filter
909 motorsport leads
Mocal oil cooler
Full samco boost, water and ancillary hoses (blue)
Radtec rs 500 intercooler
Radtec alloy radiator
RS 500 turbo damper
Grp a ramair cone filter
909 motorsport leads
Mocal oil cooler
Full samco boost, water and ancillary hoses (blue)
Radtec rs 500 intercooler
Radtec alloy radiator