There are some things that don't match up to historic values. The fact that they are hard to describe, harder to test for, doesn't negate the fact they don't match up. Like having A6Ms that can follow hellcats in dives, or can zoom up 5000 ft or what have you. Or very draggy I-16s being able to dive on and stay on faster craft in chases where they ought to fall behind quickly. (these are just examples)
The hurricanes have amazing dive and zoom climb performance, coupled with no risk of stalling, very generous roll rate, and top that off with quad hizzos on the IIC, and you get a total package more than any comments or performance capabilities I've read about for the real craft.
going back to your mention of the speeds... Maybe we don't have the 100 octane? I thought we got it for the Hurr1 same time as the Spit1, but going by the following from wwiiaircraftperformance.org:

compared to:

Interesting to compare. Maybe HTC was going for 87 octane? Doesn't explain the dogleg 2nd gear on the charger, but might explain some of the rest? Also the fade-off on the IIC power curve above FTH also looks abnormal. Also interesting to note that despite different supercharger the IIC had same low-alt speeds on the deck as 100 octane Mk.IA.