I can't help you with your PC upgrades since the game is not fully optimized yet. There are people with mid-level PCs getting good results while others with better ones get worse results, players are tweaking things on their own ranging from config files to mods, etc...long story short there's no common standard yet to know exactly which upgrade will give the best gain in performance, so it's smarter to wait a few more weeks before making decisions
As for level flight, not all aircraft have a complete trim set. Some have aileron and elevator trim, others have rudder and elevator trim and the 109 only has elevator trim.
So if you are flying a Hurricane for example, you can correct the yaw with rudder trim and the climb rate with elevator trim, but you can't do anything about the fact that it's slowly rolling to the right. You will have to correct it yourself every now and then.
However, this is not a mistake with the simulator as these aircraft were like that in reality. The game only gives you the same controls a real pilot in the real aircraft had.
I think the only aircraft with full trim capabilities are some of the Luftwaffe bombers (they even have autopilots). Everything else can still be trimmed to make flying more comfortable (less use of the stick during cruise), but it won't fly hands off in a completely straight and level attitude for more than a few seconds.