Hi Pampel,
How are you going in your decision?
I'm the manager & a coach at Cronulla SUP, I've been riding the JP Surf Wides since Jan this year. Mostly surf beach breaks & ridden majority as a thruster.
I was on the 9'2 JP Surf then dropped to the 8'2 Surf Wide which opened up a whole new world of surf SUP for me. It is really stable, able to generate speed down the line really easily & so much looser than the 9'2.
I've ridden a heap of boards in the last 12 months including the Naish Raptor 116L, JP Slate 7'6, 8'0 Hypernut & 8'2 Fanatic Stubby.
Although a different shape compared to these vanguard types I think the 8'2 Surf Wide has a fantastic balance of stability & manoeuvrability.
For you I think it depends how much you want to push yourself or if you want a board that will allow you to progress & improve but still provide good stability, the 8'8 is still a good drop in size & volume from your Slingshot.
Pics below are on the 8'2 just over a month ago.
I was 98kg pretty much the whole time I was on the 8'2 & dropped to 94kg recently.
I'm now riding my new board, the 7'11 Surf Wide, which is 106 litres & absolutely loving it.
I'm 34, been riding shortboards for 22 years, been riding SUPs for 3.5 all up.
Good luck with your choice, I think you'll be really happy on either the 8'8 or the 8'2.
Cheers, Larry