RE: Early planning alternatives for light weight sailors
My experience with the wider boards (starting with the Starboard W-75 flapper board, then the F-155 (85 cm wide) and on to the 100 cm wide pure formula race boards) is that it takes a bit larger sail, to get the wider boards going in truly marginal conditions, but no board I know that's less than 85 cm wide with stay on plane when the wider boards will.
Getting a narrower board (< 85 cm wide) going in marginal conditions requires more pumping to "launch" and alot more pumping to stay planing in the lulls.
There are some narrower boards (the Hypersonics, '04 Free Formula and '05 & '06 F-Types that will stay on plane as well as a formula board and are alot easier to sail and do not requie the hugrigs.
But, it deends alot on the sailor and the rig choices.
Do you have a rig that's race" oriented" or something with substantially more low end power.
Do you mind pumping or is a couple of big pumps to "launch" about all you want to do.
No clear and easy answers to this question.
Hope this helps,