When I was young we moved a lot, so I had 2 new schools in 2nd grade, 2 in 3rd, 1 in each of 5th, 6th, 7th and 8th (which was a killer as we moved states, and where we moved from had 7th in primary school, while 8th was 2nd year high school in my new school, so I missed out on the first year of many subjects). It is much better to move at a break - like the beginning of high school, because kids are automatically remixed at this stage, and it is much easier to make friends.
I would go with A, and if you are not FI by this time (sounds like your worst scenario would be 2 years later - which might be 4 in B), be prepared to go with the B option. Really, really try to be FI by the time you move - maybe this will give you added incentive!