Cooling System - revisited

The journey to Donington and back again showed up the limitations of my cooling system re-designs.   Pottering along at 50-60mph, as I normally do, and the temperature was perfect.  But once I started accelerating hard and doing 70mph + as I had to on the Memorial Run, I found she overheated again.  Also my legs go very hot as the air was coming out in the footwell.   A number of people on the Club Forum have pointed out that people always concentrate on getting the maximum air flow through the radiator, forgetting that you also have to provide somewhere for the air to escape as well.  So I think my problem is that while I have enough air going through the radiator but at speed it cannot escape from the engine bay so just backs up and slows down the flow through the radiator.

So I need to figure out an escape route for the air.  

I already have lots of small louvres in the bonnet but apparently they are not man enough for the job.

I could try putting some larger louvres in the side panels

or a large hole in the top of the bonnet.

More research needed.