OK, I refer to the BMWCCA / Bentley publication 'BMW Enthusiast's Companion' page 81. Inter alia 'substandard radiators from Behr Radiator of Mahwah, New Jersey.' Also 'BMW radiators are too small in capacity and a constant source of grief to owners.'
Ben T wants to race, high rpm (horsepower / heat). Although he has not quantified the higher gauge reading or changed the sender he thinks the engine is running too hot. By all means change the water pump, thermostat, radiator cap and hoses but for his application I believe a larger radiator is prudent.
Having crewed for a race team in Western Australia (it gets hot here) we ran oversize radiators compared with the same engine in road use without problems. Also from his OP his gauge is not behaving normally - change sender.

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E23 735i; E30 318i; E32 735iL; E38 735iL; R50 Cooper; R55 Cooper Clubman.
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