I think your paint chipping is good - it's easier to underdo it than to overdo it, mind you.
The wing on the top drawing lacks the level of weathering of the fuselage, but you've corrected that on the lower drawing. Don't forget to make the tire dirty. I would also add some reflection material to the canopy: this will enable you to "shape it" more. The Spit had a nice rounded canopy which deserves the extra work.
Keep up the good work.
As for the RAM, I have 480 Mb (512 - 32 for the video card ...). When I started I only had 256 (-32). Maybe I'll ask for some more RAM for Christmas. I think I'll blackmail my fiançée: another 512 should be cheaper than that ring I just bought her...
But if it makes her happy, it's worth the money.
