I've always found larger sails ( 6.6 + now 7.2m ) hard to pull on and very uncomfortable and tiring.
Light bulb moment 1
When I was trying the 7.2m it was set up with the harness lines further back than I usually use ( c 5" further back! ). I found it worked well. The main reason mine were so far forward is that with the big sails I am often sailing in subplaning conditions out of the straps and standing up near the mast. I found I could still do that with the lines further back.
Light bulb moment 2 -
I had the boom at the bottom of the cutout ( I'm 5' 6") so it was about chest to chin height like I usually have it. Someone who knows the sails and better sailor than me pointed out that the centre of effort in the sail was higher than where I had the boom and that would make it harder to pull on etc. We raised the boom to about eye height ( middle of the cutout) and lengthened the lines and it felt heaps better.

The only problem now is that works for the sail at the bottom of its range but to get max downhaul I need to put the ext up a hole which made everything feel yuck again.

I cant remember where that made the boom have to be..? So the boom is even higher..???