Some good TV here for Tones and others (I assume it's good, I haven't seen it yet)
http://www.bbc.co.uk/iplayer/episode/b00jw9cw/jim-clark-the-quiet-champion
I have enjoyed this documentary a couple of times. I was at a hillclimb at Harewood helping out a mate when Clark was killed. It was announced over the PA and total gloom descended.
It could be because it is hard to have a hero you know, or just my age when he was the best, but for me Jim Clark is the greatest racing driver ever.
He won more than 1 in 3 of the Grands Prix he started.
All very well quoting how many races total, or how many in one season, but the hit rate is more indicative IMHO. Nowadays we have almost double the number of races and the cars are much safer so careers are longer.
Fangio and Ascari have better hit rates, but back then the car won and if Fangio's car broke his team mate would be called into the pits and give his car to Fangio, so not quite the same (or maybe I am biased by the teenage fan thing).
Of the drivers racing whilst I was in F1 I rate Senna highest personally.