Urchin,
Yeah, the La-7s and P-51s and Spit IXs and N1K2s and Spit Vs and ect, ect... can all beat the Spit I easily if they know what they're doing. Ths Spit I is so crappy in the high speed handling that if anything gets you a little fast they can out anything you.
That said, I'm 6 and two against the Spitfire Mk IX and 4 and 1 against the La-7.
16 and 16 overall. I'm having trouble even managing an even K/D ratio in the Spit I.
About the Mk V, I don't know if it out truns the Mk I, but it certainly out engines it. I had one pull a yo-yo and I could follow. He killed me.
One thing about the turning on the Spit I is that you quickly realize how important turning speed is, not just turning radius. The Spit IX or N1K2 can't match they radius of the Spit I, but they can easily turn more degrees per second due to their higher speeds and better engines.