Hardpole, I take it you haven't done ether. The ledge to lanno has been done in 25 minutes and the last couple of times I sailed back to ledge to get my car,no comparison. To sail from warnbro to scarbs in the same time you would have to average over 160km per/h, it's about 4 times further.
I think scarbs to lanno could be done in a long day but the more people you have the more chance of something going wrong, it only takes one slow person to hold up the group.