performance with large rules files

[Ramprasad]

I posted this a few days ago , sorry for reposting 

 We scan mails for quiet a large number of domains ( around 1.5k
domains). The scanning happens on multiple identically configured MS
+postfix+SA  linux boxes behind load balancers

   For every domain that is added there will be entries in
spamcheck.rules spamaction.rules etc. Besides the domains will have
their own whitelists and blacklists which go into whitelist/blacklist
rules files. Already these have more than 10000 lines  each

Obviously the easiest way to scale would be to break the architecture. 
Have first set of domains on one set of machines, next on another , ..
etc

But that creates a maintenance problem. Today with identical servers ,
maintenance is relatively easy .. If I have non identical configuration
I may have more problems managing servers 

Thanks
Ram