I tell you what I played a hunch and bought the A300 earlier today. I must say the performance is stable in terms FPS and overall stability. I did introductory flight from EGSS to EGLL (inbuilds scenery) and I was getting reasonable performance. Compared to A310, I definitely noticed difference as to how they fly. I find A310 quite jerky on controls, The A300 is just about right.
The drawback I found is the sounds, I think Sounds update would be awesome.
I am going to attempt a full flight later tonight and see how this bird performs.