Hi Robert,
The 75kg is a "never exceed" limit - so you should aim for a sensible value that is below that figure.
How much leeway you give yourself is one of the things you need to assess - and as Roger suggested, we regard the main awning fabric bag as a sliding balance weight.
So is 53kg OK or would 65kg or 70kg be better? I think the answer depends on the caravan, the tow-car, the weather conditions, and how the caravan was built and how you load it...
For us, towing a German Eriba with a MTPLM of 1200 kg - the recommended nose-weight multiplier is 4% - so we try for a nose-weight in the band 40kg to 50kg depending on actual load (with a 400 kg payload we never get close to even 1000kg)
And as you seem to have discovered there was little apparent difference between 53kg and 75kg - stronger sidewinds might alter your perceptions though...
Robert