Hi Coreyb,
The stability is a function of the design of the board mainly the rail shape and where the volume is placed helps alot.
A lot of the popouts are multifunction boards SUP/ WSURF and as a result will not perform the way you want them to.
You can get dedicated 8'6 SUP boards that have great stability like the Surf Shapes, Dale Capman, Laguna Bay and PSH . Yes they will yaw from side to side when you paddle but you will over come that with time. Also you will need to take off later and closer to the curl so timing needs to be good, but hey you already ride a short board.
Rod Hocker Surf Shapes seems to have found a good mix of volume paddle ability,stability and from personal experience last weekend I can say the boards rip or the 9'4 x 29 does.
I am a larger unit at 105kg and was able to stand stationary on one of his 9'4s in 20+ knot offshore winds. I found it relatively easy to paddle on to shoulder to head high waves, but I had to make later drops.
The volume numbers appear to be 1.3 to 1.5 x your body weight for ripping and 2 x BW for starting out.
Fins also play a large part and will radically effect the way the board surfs if it has been shaped for performance.
The hard core Comp Boys seem to surf Laguna Bay Customs sub 9.0, Surf Shapes Customs down to 8'6, Paddle Surf Hawaii Rippers and Customs, Dale Chapman Customs 8'8 ish, Naish 9'3 and may be soon the sub 9.0 range. If you can get one the Magic Carpet Luke Egan sub 9.0 are alo supposed to be great.
Hope this helps.
Phill.

