This one was harder (for me, of course). I got all sorts of pains, cramps, sweaty hands... its physically demanding. But mainly, it completely forces you to do things you are not prepared to do in a car. I mean, you have to learn how to drive all over again. Its too crazy, as it is awesome. Still, ff you manage to sprint for a minute or two, you can cruise for the rest of the lap, real safe, with room for mistakes, and still get gold by -30sec, which is what i did.
Do you know which challenge made me feel exactly like i did in Mission 34? The S-5 Mission (GT40 Mk1 @ the same ring). S-5 has an added challenge - you can't touch the GT ahead of you, and he might get you out of the race when behind you. I honestly thought that it was just as hard as M-34.
In my experience, this is my current rank (for gold times):
1 - Seasonal SRT X (GT6)
2 - Senna's 97T @ Brands Hatch (GT6, final challenge)
3 tied - Mission 34 (GT4) and Mission S-5 (GT6)
4 - Vettel's Red Bull (GT5, final challenge)
5 tied - Test IA-15 (GT4, 190E @ the ring) and IC-10 (GT5, 512BB @ Rome)