Hi Andy,
Funny, I just used 1250/68cm fuselage and 1000/60cm on my new Sky Style 4'11" /75 yesterday at Worthsee - so with the 1000/60 2/3 forward of centre (new boards have the boxes further fwd), the mast/foil felt very balanced. With the 1250 in the same position right afterwards, I have too much front foot pressure.
So would suggest when using the 1000 to move the whole setup 2cm further fwd, this should work well, vs the 1500 position. On the 5'0" you have, used it fairly far fwd, close to the front of the boxes for max pop/lift with the 60cm fuselage.