Hey Tim. I don't disagree that tuning is as much of an art as science. In another career I was tuning Java stacks left and right for Websphere and ColdFusion.
However, with regards to tuning CoreXL in an environment like this it is all guessing at this point in time. Check Point should have performance metrics for their gear. I don't see why, if given a cpsizeme report of sufficient length for a given configuration (blades, hardware size/build) and a known variable such as "my new security group is built like XYZ" and "We plan to do ABC with the rest of the environment" they should have a calculator as to what to use as a good starting "guess".
So, as a discussion point:
Hey, CheckPoint, I'm running Application "Super Awesome" on a clustered pair of 15600's with blades AV,IPS,IDC,AB, with X amount of bandwidth and Y amount of traffic slow and CPU is XYZ and memory is ABC (and all of these other values you can get out of cpsizeme."
I want to move "Super Awesome" (and insert other applications/gateways here) to a Maestro solution with MHO-XYZ and backed with X number of ABC gateways with a given set of blades enabled.
Plug all of that into a calculator and it spits out a value for CoreXL to start from.
I don't see why that would be so hard since they have all the metrics.