I have the 8'2 x 32 jp and am very happy with it. Great for stability when there is a bit of chop. Havnt ridden the starby but for my next board I'll prob not go any smaller in length (even maybe slightly longer) but will defo go a bit narrower, but not too much as 80% of the time I surf it in choppy mush!. Depends on your weight, surf conditions n experience I guess, I'm 73kg n 5'10
I never padled the JP but did own a WP8.2 and tried the WP7.8.For me, 90kg in onshore beachbreak with current and shifting peaks and not so fast waves (so crap conditions) the 7.8 was really easy to paddle but a bit harder to catch waves with. The board has some rocker and is rather short for my weight so it wasnt a really glide wonder. Once you got on a wave its a rellative snappy fun playing thing.I wowned the WP8.2x32 wich catches waves a LOT earlier and is quicker to paddle due the extra length and its so stable you gonna doubt the length while still more as radical enough for the given conditions.It might be a weight thing due my 90kg , but to me the WP8.2 felt more harmonious shape wise as the 7.8 to me.Nowadays I have the Airborne8.8 for the conditions mentioned above because no matter how fun a really short board is, you need to catch that wave first and the bit of extra length helped with the glide, while in good conditions in holidays and a very seldom non-dutch day I grab my 8.5 Pro (both the BC version).