Jenex is offering a "9000" series rollerski that has a 100 mm ratcheted
wheel up front and a 900 series wheel in the back. Shaft is
effectively longer than 900 rollerski. The setup I have has a 910 wheel
in the back and speed reducers.
The ski feels great. It's nice and slow and overall feels like it
gives a better workout than a 900 ski. Also, feels more ski-like in
general. Len's partial explanation is that by having a narrow wheel up
front and long shaft, most of your weight is on the rear wheel, so to
get the ratchet to engage, you need to press down more than you would
with a 900 ski.
Also, biggest benefit is not having to worry about having the front
wheel locking up. The 100 mm wheels rolled over things I wouldn't have
expected and the little killer pebbles have caused no problems so far.