Hi Tanzi...
I am older and heavier than you (67 @ 100 kg)
All I can really offer is my opinion of what makes the Speeed work for me, and some random thoughts.
In summer, I have no problems on the 8'10 Speeed... so considering your age, weight and the fact that you don't need to consider winter gear, the 8'5 Speeed should be very easy for you after the initial adjustment period.
I know that I would struggle more on the 9' Starboard Pro because, although that dims are very similar to my 8'10, the pointier nose would translate to much less stable for me.... having said that, at 37 and 90 kg, the pro should be easy for you.
The question is how you like to surf.
The thing that drew me to the Speeed was the way the tail carved so sweetly.
It has never let me down.... in all conditions the Speeed has a crisp, tight, driving carve off the tail, that rocket you out of a turn, and tight cutbacks, without scrubbing off speed.
I bought a 9'5 for my winter conditions, and was a little concerned when I took it out on a 2xOH hurricane swell. It was amazing.... handled the biggest wave I have had in years with ease and the carve off the bottom was solid and tight. It never felt like a big board to me.... so Bert Burger has done and admirable job of making this design work through all sizes. The XXX construction has a unique "give" built into the bottom of the board, that translates into an extremely smooth and vibration free ride, while the deck is super hard and tough..... a perfect combo in my eyes.
The Speeed is fast and effortless. The wide, scoop nose is super light and effective, as well as providing the "takeoff" stability I need. On pointy nose boards, I tend to sink the nose as I drive into a wave, which means I can't "forward weight" as much as I can on the Speeed.
I have ridden many sub 9' boards in the past 2 months, including the 8'2 Wide Point, 8'8 Airborne, 8'8 World Wide.... mostly traditional shapes, but I am always glad to get back on my Speeed, but I have never ridden the Starboard Pro... it looks like a great board, so I can't comment to it's performance. I have owned a few Starboards and have always been happy with them.
The Sunova Soul is a more intermediate shape..... the performance Sunova's are the Acid, Speeed and Flow
I have a 9'2 Flow on the way, so I will be able to comment on that, by the end of December. I have never seen an Acid but I hear good things.
Another, though..... my buddy, who is 40 @ 72 kg, also has an 8'10 Speeed and loves it. The design is so consistent, that I jumped 2 sizes for my winter board and am quite happy..... so don't overlook the option of going with the 8'10 for comfort and ease, without giving up much performance, if any.
Here's a pic of my 72 kg friend,laying one over on his 8'10 Speeed