First, are you sure it is the Spring Webflow causing the issues? I
would suggest using a profiler to find out where most of your
bottleneck is.  I've been using EJP <http://ejp.sourceforge.net/>  for
a project at home because its free, and it helped me speed up my
project by 60%. I found out that while there was some slowdown where I
anticipated, the true slowdown was somewhere else entirely (and it was
a lot easier to fix).

Although EJP has been helpful, it has some performance issues itself,
so you might try it out, and if it doesn't work for you, get try a
different profiler.

In any case, we use Spring at my work extensively, and performance
hasn't been an issue, although I suppose it depends on a lot of
factors, such as servlet container, rendering technology (JSP, JSF,
etc...), database layer, etc...  All the more reasons to use a
profile-before-assume approach.

Hope this helps, and good luck finding your answer.

- Daniel.