I find wider boards easier to pop off the water. Longer the board the more it feels sticky. No science just feel. Demo??

Leg pumping, the up and down motion, negates the wider board drag. That, and pure surface area, should help the wider board as you micro-reposition your feet to lessen surface area as your boat speed increases.

I think a lot depends on the riders experience and the bottom shape of the board.

A longer board may plane faster however it will need too because it is heavier 'stickier' and harder to pump up onto the foil.
A beginner may get foiling sooner on a longer board through building up speed but an experienced winger/foiler/pumper will pump the shorter board up sooner IMO.

e.g. I have 2 ONE foil SUP's both around the same volume a 6'8" x 28 108.8ltr and a 5'10" x 27.5 107ltr (the red one in my pic).
When I first started winging I pretty much exclusively used the 6'8 as I thought because it paddled better/faster it would get up sooner (plus it was easier to balance on) but now I only ever use the 5'10" as it definitely does pop up easier now that my technique is better.

Even though that board works well for winging I am hoping to get a smaller wing board soon probably 5'

Thanks guys, I just think if there's a point of negative returns after some short point as mine is 4'10 ie. much shorter than 6 or 7' boards campared here and would be much more sensitive for diving etc. when pumping. And I'm only talking about lightwind capabilities. But yeah, I guess just more technique is needed...

Because you want better planing, you need to look at tail design.

When everyone rode super LIFTY foils, we could "pump" onto foil before the board ever reached planing speed. So anything that was short won the race to get on foil because short pumps and unsticks easier.

But that all takes skill.

Lacking this skill, a newbie wants a board that planes first, then comes onto foil.

But now, experts riding ultra fast thin foils, also want a board that planes first, then comes onto foil.

Indiana Paddle board offers a planing first board design.

Not sure if you've tried footstraps, but having the front foot straps makes pumping way more effective, in my experience ;) I ride 5'0 Sunova 76ltrs... Axis high performance surf 860 wing (1200 surface area) I weigh 87kg...