First and formost, I salute you for your effort you put in coming this far.
If by now you cannot improve any further in lap-times running the fbm, here's my top-tip: take another car.
XRG and XFG are open to demo-users, so take either and feel the difference.
Although I now own a G25 since about a year or so I still quite often just use mouse when going for a quick spin in the road-cars myself. If you have set up your controls the right way that is...
...fully-linear steering, gas brake
...no "helping hands" of any sort
then you can go a long way using a mouse except in a F08 or BF1 for that matter, they are just un-raceable using mouse because of their insane power-to-weight figures
...another thing that you should check is the sharpness-settings of the textures in the graphics/display options. I just recently explored that the long-kept defaults can be signifficantly improved allowing for much better visuals of bumps, road-surface and curbs.
If going for a wheel, please consider one of the newer 2nd-generation Logitech Driving Force
GT's if your budget isn't on par with a G25. They are marketed for Playstation-3 but work just fine with a PC. Check out a short review at insidesimracing
http://insidesimracing.blip.tv ... vingForceGTWheelReview593
Having a higher usable steering lock is of GREAT advantage over a cheap'n'cheefull Momo-Racing (the still available black one). Especially when it comes to any road-car or GTR. I am talking out of experience since I had one of those myself.
Keep in mind though, that -in the old days- the pedals of the cheaper Logitechs tend to wear out after a year's worth of intense use or so. People say that newer revisions should have improved substantially - but tbh: I'd still have an unsound feeling about them.
The G25's weak point on the other hand is the h-shifter. I already hat my entire set replaced because of this little accessory going bust for no comprehensible reason whatsoever (and I do not throw my kit against the wall, never!).
One other thing I might suggest is: get some fresh air before getting frustrated. Plus: Go and dig up some 32 british pounds in order to aquire an S2 license. Sounds as if you might enjoy one.
Cheers
DrBen