I have Concertos. I like my Concertos. I made a huge jump from basically Jackson pond skates (maybe Mystique or something, had a plastic sole and the old style MKIV blade) to my Concertos. Supposedly my Concertos are extra stiff from the factory (seller told me by 30%,) too, but the previous owner/seller is a Junior National level skater, he skated in them for 3 months doing triples, so I don't know their total stiffness now really. He said if they were too stiff, he'd send me a normal stiffness pair. His reason for selling was because he switched to size 300.
That said, they fit fine for me. I'm only on waltz jumps, but I'm a 195lb guy and need basically heavier boots anyway. I wore those old Jacksons down from brand new, 4 months of skating I ripped the sole off the leather (and then skated another 8 months or so via repairing it myself with screws at home.) So it might be a different situation if you're a relatively light girl in them. As far as their stiffness, they don't feel overly stiff to me at all, and I'm even lacing to the top with them. They feel secure, but not stiff. And again, mine are supposedly stiffer than they are normally. I have no "overbooting" issues coming from them at all. I just leave the top hooks a bit loose so I can bend my knees enough, and I'm fine in them.
They run pretty true to size, I think. I have 290s, and my feet measured 280 and 285 on a ruler (though not diagonally.) I might have bought 285s brand new if I had the cash, but the seller sold these for 160 on ebay, and I tried them on not on the ice and they seemed fine, but on ice it wasn't as tight as I like, though. But, 160 vs $700... The looseness isn't like, a whole size difference, ie, size 9 to 10 or something, but if I get to a level where the tiny tiny bit of difference really matters, I might switch to 285s and maybe get Ice Flys. But at my level it's basically just nitpicking. And I could try on a 285 and think it's too tight, who knows. As far as fit, they have a fairly narrow heel, and quite wide toe box. For me on my right skate, I have some pain on the side of my heel from it being too tight, so I'm gonna see about getting it heated eventually. For now I just tie a bit looser. Then again, I've only skated in them for two weeks, so this all might just be standard new skate break in kinda stuff, I remember similar type things with the Jacksons I had, just the Jacksons were legitimately too small, so maybe I'm just used to skating in small skates? Who knows. Maybe it's just me thinking "They're the wrong size because your toes don't hurt anymore!"
Lastly, as far as weight, I can't speak for the Ice Flys, but my Concertos are comparable to my PVC soled Jacksons in weight. The Concertos maybe weigh a tiny bit more even. Ice Flys will weigh less, but I think because the Concerto is a more "traditional" boot that makes it weigh more, but still less than equivalent skates of other brands.
So if you like the Ice Flys and get them, they probably won't be too stiff, I think. My Concertos feel overall great for me, and I'm at a lower level than you are, but there is a weight difference, too.
Any questions about the Concertos, just ask. Supposedly the Concertos and Ice Flys are as stiff as eachother, just different boot materials.