Hi David,
Today I measured a recent;
- Tiller to be; 82cm (I am sure they are all the same, as is required)
- Carbon tiller extension to be 106cm (presume it is identical to the one you measured at 107cm)
- Ali tiller extension to be 110cm
[Extensions measured to the near end of the UJ]
I have used both extensions.
The 106cm one I have used most and is my preference currently. It can pass through the gap easily enough on tacks and I could get my weight adequately forward in the light winds at Oxford in the Winter Champs.
The 110cm one could still pass through the gap easily enough on the tacks but I did notice the small difference.