First off, yes buy the boot that fits, but hypothetically speaking if I am comfortable in both a park boot and a non park boot, what is really the difference these days. I currently have an SPK 90, it'll be my 3rd seaon on them. The whole reasoning behind getting that boot was the more upright stance, but the difference in forward lean between park boots and non park boots seems to be non existent these days.
One difference I know of is that some park boots have shock absolution while others don't, I've only ever ridden park in my spks, so does anyone actually feel a difference having absorption in their boot?
Lastly, I am 6' 2" and 220lbs, so yeah, 90 flex is too soft for me, but I always figured a softer boot is better for sketchy landings, which is why I didn't go for SPK pros when I first was getting into park. Now however, there's park boots out there with 130 flexes, does anyone actually ride park with such a stiff boot? If I didn't do park I would be in a 130 flex boot for sure.
Also, I kind of suck at park, so I'm not throwing stuff of jumps larger than 30ft really, which again is why I didn't think I needed a stiffer boot.