Desiros only draw 100% very briefly when starting away, it soon drops back to around the 50% mark, to around 40 mph, when it ramps up slightly to between 60 & 70% all the way up to 100 mph (where permitted), when the computer will then automatically reduce the power to hold it there and that's very weird when you're going downhill and it doesn't use any brakes to do it!
The power delivery is smooth and is deceptively fast and can easily catch you out, a 4 car 450 can quite easily achieve 90+ through West Byfleet from a standing start at Woking, they can easily match a 158/159, even an 8 car can, a 12 is considerably slower initially, but will get there.
A 444 is a bit slower than a 450 getting away, but get a good one and it'll not be far behind the 450 sets for performance, a 10 car 444, is somewhere between an 8 x 450 and 12 x450 for performance, again they'll be able to match and beat a 158/159 on most stretches of fast track.