For example Deus Ex (first game): http://en.wikipedia.org/wiki/Deus_Ex
This game requires a 300MHz processor, can render fairly large maps and uses the Unreal Engine for that that is powered by DirectX.

So the limit is not the graphics lib, but how you use it (as AthenaOfDelphi said). It's more a point of how can I optimize my rendering so I can render only the things I need to see in a fast way.

It you want to render large out-door area's it's possible on a low-end machine, but you have to optimize a lot!