After a good raging my engine blows loads of steam and coolant everywhere from the oil catch tank breather and the rad is down a litre+ on coolant, I can potter about normally and no issues. even blasting to 7k momentarily in lower gears but sustained high rpm in high gears and it wont pass 5k.. The boost from eaton charger creeps back to 0 too.
Head gasket? cracked head? what tests can i do before the head inevitably comes off?

You don't say what type of engine but unless your engines water passages to the inlet manifold (as per Rover K) the answer had to be off with its' head if water is getting into the oil as no external test you can do without lifting the head will tell you much.

sorry its a Yb cosworth with eaton charger on the side

well it looks like the coolant is getting into the crank case. under pressure the coolant drops and its not showing up on the outside of the engine nor is it showing up on the pistons as i look into the cylinder via spark plug hole. Hope and pray its just a head gasket issue