Sharing or separating classes & rules between virtual services

I've a rule which is used to rate limit requests to specific URIs. It does a class match against a class and goes on from there. If there are two independent virtual services running two different web services, would there be something similar to best practices which would say whether to create two near identical copies of the iRule and two different class lists and operate them independently, or to just use the same rule, and put both sets of URIs in the same list.

If we're looking at 3 or 4 entries per site, what's the likely performance hit when doing a class match on 3 lines or 8? When this is compared against simplicity of code, and easier version control, I feel inclined to just let them be combined.