Ta Genghis - it confirms my fears re the weight limits.
PS max I ever did in a T21 was 6500' - even in midsummer it was 'kin cold (both pilots wearing shorts!). And the flight previous to that had been 5400'
So parachutes could be handy in such circumstances - especially since the visibility in tight thermals with that wing like a shelf over your head ain't great
The Skylark 2 was infinitely smaller than the 4 - about 4 metres less wingspan - hence the lower weight.
A K13 with me in the back seat is getting fairly stalled at about 37 knots, as is the Skylark. A T21 can still be flying in the high 20's!