As a brief comparison between indy cars and F1 cars:
I believe indycars and F1 cars in a straight line are approximately the same – F1 cars are lighter and may have faster acceleration, but indycars aren’t far behind and may have a slightly higher top speed (can’t say for sure).
On an oval, an indycar would be faster as its set up specifically for ovals (i.e. turning only one way with banked suspension I believe).
On a race circuit, an F1 car is faster. The downforce levels produced are superior and therefore the cornering speed is much higher.
Both indycars and F1 cars have race at montreal – and F1 cars were faster.
[sorry for how vague this post is, can't really remember specifics, but I think thats mostly correct. Though please correct me if i'm wrong!]