Not sure how accurate I am about what constitutes a displacement hull but I will use the term bull nose for my reference which is more typical of 14ft race boards and DW boards depending on conditions. I have found through owning a 10ft x 33 wide all round board then a 14ft x 29.5 wide cruising board to now having a 14 x 27 wide bull nose board that on flat water the speed is much the same. The amount of litres per board is not necessarily related to weight or speed as I thought which has surprised me. My Glide was 290lt I think? Not sure about the 10ft Mana but it's less and the JL Sidewinder is 300lt. My average speed on all 3 boards does not vary that much and a lot will depend on tide in or out, wind, chop, glass it all never matches up.
Interstingly my 10ft weighs 12kg, my Glide was 17kg and the bigger 300lt board is 9kg, I thought the lack of weight would have made it faster but then you have a different rocker outline etc etc etc which all make a difference, so I would not get too hung up on litres and size just use what you like unless you want to turn pro and then they give them to you anyway.
Now in reference to shape in the nose and a DW run I learnt a bit more last weekend about that very topic. I did a run with a guy who has a similar shaped board to your but a SIC board. It was 15-18kn with some nice bumps and in sections a reasonable run was had and it was great. But no matter what I did I could not keep up with the other guy. Now he paddles much more than I do he is closer to water and must be fitter than me even though I thought I was pretty fit. I asked him about the difference and he said that shape was made for days like this, 15-18kn. It catches anything and cuts through the back of waves which I had trouble with due to practice or lack of it! He also said that if it were bigger, windier etc he would not use it at all because he would not cope with the conditions. I can only presume that a Bull Nose/ Displacement hull type would be his go to boards, he has dugout, unlimited boards etc etc in bigger situation??
The biggest difference I have found between both of my 14ft boards and their weight is the fatigue factor, I may paddle as fast but my body is less tired and strained after a 10-13km paddle. Carbon board, Carbon paddle = less wear and tear. That is enough reason for me to stay where I am and learn to handle conditions more and not worry about where everyone else is in relation to me, I run my own race for pleasure.
sorry one last thing with less weight I do catch more runners because I can chase down the wave in front, I could not do that with 8kg of extra board at a lower litre volume. Below are pics of the noses I use and they all have pro's and Con's.
Like all of us though once you get better you will buy another board and another and it's all good clean fun!