I was in the lakes around Skiddaw at the weekend. A few years ago i hit 42mph on an old M2 using 46t, the 575 is so much more relaxed
But at 67.6km/h (42mph) you weren't pedalling were you.
I've done some of the maths and I'd say that unless you only ride downhill fire roads or are a World Cup racer the times you would really be limited by a 44:11 are very rare. In fact I'd challenge most people to be able to reach a cadence of 90 in a 44:11 on a flat dirt road and then maintain it for a reasonable amount of time.
If you are reaching these speeds I'd also question whether you are using your 575 to it's best ability (ie technical stuff rather than outright speed).
But then again if you really want a 46 then who am I to argue? My only other feedback would be that the current Raceface cranks, chain rings and external BB bearings are fairly ordinary even if they look bling. X type is particularly crap and I'd steer clear of it if you are at all interested in reliability.