At 82kg, for a single board quiver I would not get too low in volume. Especially to take into account the weight of the winter wetsuit. I dont think it would be reasonable to go lower than 90 liters, you will reduce too much the length of session as you will tire much faster.
As others said, more pulled-in nose and tail will allow for more performance surfing, but I would advise to keep a generous width in the nose, kind of a semi-pulled in shape. This gives you stability, but is not cumbersome enough in turns to bother you (with SUPs, you do not perform the tight turns of a prone shortboard anyways). A stable nose also allows you to manage narrower main widths, that help for tight turns in hollow waves. You want the main width to continue 1' to 2' in front of the handle.
An exemple of the kind of semi-pulled nose shapes I love:
- semi-tomo: widths Front half-foot-off 20"7/8, main 29"3/4. Best up to a bit more than head high, too wide on bigger waves
https://gongsupshop.com/epages/box1707.sf/en_GB/?ViewObjectPath=%2FShops%2Fbox1707%2FProducts%2FGON9SUPFATPRO73- bullet nose: 19"5/16 / 28"3/4 A good compromise for various conditions
gongsupshop.com/epages/box1707.sf/en_GB/?ViewObjectPath=%2FShops%2Fbox1707%2FProducts%2FGON9SUPKARMEN711PRO- An example of what you do not want in a one board quiver (too tiring), if you are not a pro, in 105 liters like the 2 above:
gongsupshop.com/epages/box1707.sf/en_GB/?ObjectPath=/Shops/box1707/Products/GON9SUPCURVESPPRO78Disclaimer: I am a Gong ambassador, these are just examples of boards I know well, with their full dimensions for reference, this is not a buying recommendation.
Short (less than 7'6") boards are exhilarating on the wave by the accelerations and compactness, you have everything under your feet. But they paddle slower, and often have a rounder outline limiting the top end speed on a straight line and making the natural curve radius tighter. Basically a short board is better if you turn a lot, but not so great for down-the-line surfing.