Board for 75% sub-planing, and 25% planing

Currently, only the Rio S or M, Fanatic Viper 75 or 80, or Bic Core 160D or 293D are available at a decent price in my area (Quebec, Canada). I (80kg, intermediate-advanced sailor) ride on a lake with light and moderate gusty winds. I have a 140L board for relatively windy (12-20 knots) days, and a 105L for really windy (15-30 knots) days (always with major wind holes).

I'm looking for a board to use when there is enough wind for planing about 15 minutes in an hour, let's say 5 knots wind with 12 knots gusts 25% of the time. I still want to enjoy the other 45 minutes on the water, and get some speed and upwind ability in sub-planing conditions. The board will be used for beginner buddies, wife, and kids, so ding resistance is important and the EVA deck is a big plus.

I used to have a Go 170. The ride was great when planing, the EVA deck was nice, but it was very sluggish in sub-planing conditions.

For all boards, I plan to buy an aftermarket 52cm race fin and use 7.5m, and 8.5m sails. I am looking for a compromise between sub-planing and planing performance. For example, I don't expect to be faster than my buddies on old Mistral Equipes in sub-planing conditions, but I'd like to be able to keep up with them not too far behind. But when planing, I want a board that will offer far more fun and manoeuvrability than their longboards.

So which board do you think would be the best pick ?

Oh, and I have a bonus fundamentals question.
I understand that the larger board plane quicker, and the longer and narrower boards go faster in sub-planing conditions. But I see that the old Mistral Equipes, by going faster in sub-planing condition, eventually build up enough speed which in turn creates apparent wind that powers the sail enough to get them planing while I was stuck on my Go 170 waiting for a bigger gust to fire it up (everybody on 7.5m sails and similar weight and skills). So are the wider boards really planing faster ?

Thanks for your advice.