RE: Older Formula for early planning
Sounds like a very good idea to me.
Since the true Formula Race boards (WOOD construction) are a bit
fragile it may be difficult to get a really good one.
Why not look for a FE 160 from last year.
Better durability, slightly heavier, but built in a more robust construction.
May plane as early as the older Formula boards you've mentioned.
But you do need to consider the water depth.
Is where you sail going to be deep enough to allow you to use a 70 cm fin?
The FE 160 would be the maximum durability formula board for a recreational sailor.
With an 11.0 m2 KA rig you would briong your planing threshold doen to around 9-10 knots, much better than the Carve 161 for sure.
Your idea to buy an older Formula board is good, but where do you find an older Formula board that's not pretty much "used up".
I'm sure there are some around, but most have been raced and suffer from the rigors of having been raced.
Either way (older formula board or older FE board) you will be planing a whole lot more than on your Carve 161. You will however need the big rig to make this all work.
To get really early planing for a 90 Kg. sailor you will need at least a 10.0 m2 rig. Get something powerful like a Retro or NP V8 (I'm not familiar with the larger KA sails so I don't know if the 11.0 KA if a top of the line race sail, or something more recreationally oriented with lots of low wind power like the Retro, V8, or Severne Gator.)
If you are planning to go into formula racing, I'd look at the FE 160 or perhaps a close out on last years F-160 Formula board.
But, remember, if you go with the formula board, you will definietly need to go with the bigger heavier formula rig and a min. 65 cm fin.
Hope this helps,