2
It all depends - do you know, why the site is slow? Is it the server response time? Processing time? Transmitting time (bandwith)?
If it is the first or last, I don't see how it can be done.
If it is the second, I guess it is possible to insert some checks to evaluate whether a certain limit has been reached and then redirect - but where those checks should be or how they could work, I don't know.