A few 6970 and 6950 users reported that they can run their game at full settings, quite a few 6970 users even use multiple screens so the rendered resolution is far higher than say 1920x1200, which is what I am using for example.
Many of them also have a sandybridge CPU however so I am not sure how much it will help with an older CPU: the new career mode is very taxing and the CPU is a bottleneck there since all the AI calculations are done locally, in MP the server does all of that.
The game has been optimised very well and they have optimised it again and again over the past few updates but the clouds are really eating my FPS, and I already upgraded from a 8800GT to a 5770 last year, I still go below 40FPS at times but I guess that's not that bad.
The learning curve is not that steep.
Imo that depends quite a bit on what you fly and where though
Some excellent pilots play ROF, many of them were incredibly good 1on1 and 2on2 pilots in il2, and chances are you are going to meet them online

Many of the rotary planes in ROF are very manoeuvrable due to their low weight but they are also fairly hard to fly due to precesion of the rotaries, center of gravity issues, in some cases the wing profile etc so learning to fly those efficiently will provide a relatively steep learning curve. The two triplanes and the camel are affected the most by this, but at the same time they are also some of the best planes, though the Sopwith Triplane might be a tad less impressive than the Fokker Triplane.