Your PC should be able to run Cliff of Dover quite nicely. As for recommendations, a bit of a minefield as there would be someone upset whatever I say
If you are in to WW2 and that era of military aviation, then you should give IL2 Cliffs a try. If you want more of a study sim, as in depth of the P-51 type then ED's plane is excellent. Both sims are really in beta, although the DCS one is up-front about it.
An alternative would be Gaijin's Wings of Prey, as that looks great and is fun for a quick blast ($5 on Steam etc). BoBII WoV is also worth a look for excellent single-player play and great AI.