cSe - my stats aren't too dissimilar to yours (just a little shorter) & like you, I've been through a similar 'board hunting' exercise trying to fine-tune my quiver. I currently own the 8'5 Speeed which is awesome when it's calm (by far the most fun I've had on a SUP) but I do struggle when the wind/chop are up although I'm confident that with practice, this will become less of an issue.
Like Kuz/STC & many other Seabreezers, I'm a big believer in the magic of the Speeed shape (as you know, it's like 2 boards in 1) so I've also ordered the 8'10 which I plan to use when my 8'5 poses too much of a challenge + my other half can use this board on the rare occassion she joins me for a paddle.
I also opted for the 8'11 x 30" x 120l Acid (I ordered this shortly before the shape was fine-tuned) however I've yet to put this board through it's paces. I bought this board as a replacement for my 9'2 JP Surf Pro with the objective for it to offer me a different ride vs my 2 x Speeeds. Kuz has spent a lot of time on his Acid so he's well placed to answer questions on this board but from our discussions, he firmly believes the Acid is a versatile board & shouldn't be stereotyped as a high performance 'only' board.
The only downside I can foresee with my quiver is that I still don't have a super stable board so either I have to pick the days I go out or I need to lift my game....probably a combination of both.
I personally reckon that for the average punter, the Speeed is best suited for more cruisy turns however guys like JohnnyMaya/JC/STC have all demonstrated that the board can turn on a dime if & when the need arises. Looking at JC surfing the Speed/Acid & Flow, it's hard to draw a comparison for us mere mortals however from where I'm sitting, it looks like it's easier for him to get verticle pivot turns with both the Acid & Flow vs the Speeed. Clearly the shape of these boards help facilitate this.
As Seajuice mentions, the Soul will no doubt offer the best all-round charactersitics for for the majority of us. I guess choosing the correct size & shape comes down to personal preference i.e. I personally don't like boards much over 9' x 31" & I reckon 120l is about the right volume for me (still enough to pose a challenge) so in a perfect world, I would love to compare the 8'6 Soul vs the 8'10 Flow vs the 8'10 Acid. Possibly the 8'11 Soul would be a great option for a really stable all-round board?
Bottom line - I've had exactly the same questions as you & I will certainly post a comprehensive review on all 3 of my Sunova boards (hopefully within the next few months) however in the interim, it would be great to hear from someone that has compared the Speeed vs the Acid vs the Flow vs the Soul....or part of