I play it like a typical P51, just with a more boatload of power. My routine is generally climbing towards the 4k-5km alt region or higher at 290-300kmh IAS, mostly dependent on my team and enemy composition (am I fighting against early jets + prop mix? Or full props?)
If you use Manual Engine Controls, the P51 line are the easiest to manage. You can leave your Radiator to 100% and you will barely feel the effect of drag. Oil temps are the one you should be wary of though, but you can mitigate this by laying off WEP or lowering Prop Pitch to at least 90%-95%.
Now, the P51H is an actual demon and performs really, really well in most disciplines. The WEP is amazing as shit, you have outstanding straight-line energy retention, vertical energy retention, above average horizontal energy retention (Though, your turnrate only good for medium-high speed, YOU still need to be careful.)
For Germany, you beat the 109’s and 190 in any metric, but the Ta-152H can GIVE you trouble, it outrates you in a sustained, but try and fight them in the high speed. You are faster than them though
You beat Griffon spitfires, they outturn you though, and the LfMk9 can be a headache but I am certain you can beat them in a high enough altitude or in a high speed duel.
Late Yak’s are troublesome to deal with. They’re agile, fast, maneuverable enough. Be conservative around them, they rip and compress in high speeds.
Japanese, well… you already know, you outspeed them, but you don’t outrate them.
Overall, you need to be adaptive on what is currently going on. Go for the highest fighters if you can then ladder down. BnZ, BnR, HnR or whatever, you are really good at anything. One thing that always irked me is P51H’s going for bombers. Ignore them, go for fighters first. It helps your team more.
Remember, you have limited WEP, atleast 11 minutes I think? So becareful and know when to use it, AND you still have that annoying rudder quirk that happens in high speeds.