R5FORD, I'm new to this forum but your original comment was :

"there not that quick at all tbh my ST with a exhaust and remap will destroy one"

I assume that your talking about the 5 pot turbo focus model known as an XR5 in the Southern hemisphere. If this is so, IMO there is no way a remap & exhaust only, will reap a flat 5 sec 0-62 mph unless the tuner would be prepared to lean it out to the extent that the engine would likely blow up. Run it and tune one for 107 octane race fuel and they could be equal.

I agree that a Cosworth with equal power would beat an XR6 turbo due to the power to weight ratio. At what lower power point with the Cosworth they would be equal I can't comment on.

I'm sure its been said on this forum before, but with a big wallet you can make anything go super fast.

Also from experience, peak power and weight aren't the only consideration to performance.
An example - the HSV325GTS (VXR bathurst) produces 325kw at engine and weighs 25 kgs more than my 270kw XR6 Turbo, yet the XR6 is slightly faster to 62mph and consistently half a second faster over the 1/4. Put this down to the broader torque curve supplied by forced induction.