Take a look at those charts and you will see that the shaded portion under the curve, is basically WEP if you read the discriptions. The non-WEP max speed is 338mph if I'm reading the chart right (my vision is somewhat blurry due to recent multiple eye surgies, and the later in the day it gets, the more tired my eyes get). You can test against that value if you wish.
In most every case when looking at aircraft data, max speed means just that, the maximum speed an aircraft under its fastest condition. But as with anything there are exceptions.
I just looked at my chart again, and it reads that the max speed should be 350mph, not the 355 I typed in earlier, I misread the the charts fine lines. Sorry for the mistake.
On my FE the red tick mark is just starting to edge over the 350mph mark. In other words the red line's center is directly on the 350mph mark, while its leading edge is past the 350mph mark. It may differ very slightly from video card to video card, and resolution to resolution, but I don't know for sure. But I do know that HTC uses a version of the FE that has a digital readout to test the FM's.
Regardless, its very very close on my computer.
The charts I posted are basically data directly from Focke-Wulf provided to the Luftwaffe high command (but translated too english after the war for this english translation). I have no idea how Brown or others got their data, but I've seen other similar data charts originally from Focke-Wulf, so I tend personally to put my faith in them rather than from other sources. Unless someone has the original charts in German, and they show something different, I would tend to think its about the best source of data you can reasonabley get.