That very well may be, but I have not seen a commercially available CNC head that approaches any of those numbers. The exception might be the Bloomer head, but that also has a lot of hand work from my understanding, and they command a premium price. I'd love to see a list of people that rework SBM heads and what the resulting flow is and at what cost, but I don't think something like that exists and most of the good shops that do porting don't advertise costs. Getting someone to answer a phone to get a quote takes forever. I was considering a trip to Pennsylvania but you've stated you aren't taking on any more work. I'd rather not spend $$$ shipping the heads around.
I think a member up in Canada was having a set of the Shockers worked over by a guru and got some significant improvements, but that was with hand work and it didn't come for free.