So I'm not a particularly accomplished skater (pre-silver dances, 2nd test and Juvenile Free with an axel and inconsistent 2S back in the day), but I've been doing it a long time. As an adult, I've been curious, and tried out different blades. Here's my take for what it's worth.
I grew up on CorAce and Profs. My last blades as a kid were Profs. When I came back to skating, I switched to short blades (vision Synchro). I the length, or lack thereof, didn't bother me. And tbh I don't know if a 1/2" difference in size translates to a 1/2" difference in runner length. BTW- the Edea boots have a higher heel (which is why they require shorter blades). THAT you'll notice, because it will push you more onto the front of your foot. This is not necessarily a bad thing, a lot of people like it, just giving you a heads up.
I've also tried 8' rockers (the Ultima Supreme). I didn't notice the difference in the back of the blade (where the 8' is). Nor did I notice the side honing (which is what I was most curious about). My take home= I am not skilled enough to need those minute differences.
I personally notice spin rockers most of all. The geometries are different on each blade, but haven't met one yet that I find unusable (except on some MarkIV's I tried....). Spin rockers have a tendency to flatten out over time with machine sharpenings, so that's mostly what I feel/have to learn when I get new blades. My guess is that's what you'll notice too- it's the most pronounced curvature on the blade, and right under the ball of your foot.
Fwiw I have also discovered I am picky about toepicks....far more than I am about 7'or 8' rockers.
As for moving to an intro-competition blade. I would say do it. When I was a kid, as soon as we were out of rentals we were on MK Profs or CorAces (MK and Wilson were the only brands at the time). With the exception of financial reasons, I don't see why that would change for adults. I think you'll appreciate having a decent spin rocker. I honestly wouldn't sweat the 7'or 8' rocker.