Uptown:
IMHO, 1-2 mph is not worth complaining about,(although see below), the strangely porked turning and flap performance has been noted for a long time now by Widewing and other quite knowledgeable folks, so apparently is not going to get changed anytime soon.
You're seeing something of the attitude problem a lot of simmers have with the Mustang though. It is so popular and they've been beaten over the head with the "best plane of WWII" stuff so much that it has shell-shocked them and made them bloody hostile towards the thing, almost glad for it to be modeled as a dog.
I can tell you though Uptown, if the thing was a little faster and turned a little better, with its speed, range, visibility, decent ord capacity and accurate guns, it would cry out to be lightly perked. This would be my preference but might be a bad business model for HTC, because lets face it, conservatively 70% of new players want to fly the P-51 first and might not renew after their two week trial if the first message they got on clicking upon it was "You don't have enough points for that model".
Okay, note the P-51D-15NA doing 375mph on the deck, WITH wing racks and limited to 67" MAP.