I can think of two other people who own both a mk2 and mk1 at the same time NOW. And one that has owned both.
Smokey Mcpot has a cup and Williams. He says there is nothing in it. Maybe the cup edges it (or should that be hedges it
)
Stromba and jill own a 172 and 3 williams'. 0002 and 0200 are as quick as the 172 (both low mileage cars with less than 20,000 miles on the clocks between them), and the other williams (dont know the number, but its on 60k) is marginally faster (more run in?). So no real difference.
Enid also used to own a cup and now has a williams, and again in terms of straight line speed there was nothing in it.
I cant say how fast my williams 3 is as ive never driven a mk2 to compare.