How to improve Fmax for SOPC System?

You're off by 4ns(40%), which is quite a bit. My personal experience is that most options in Quartus to improve SOPC system timing don't make drastic improvements. (Make sure the design is constrained to 100MHz, make sure:

- Assignments -> Settings -> Analysis and Synthesis Optimizations is set to Speed

- Assignments -> Settings -> Netlist Optimizations are turned On

- Assignments -> Settings -> Physical Synthesis Optimizations are turned on(don't turn on the ones for Area)

Also look at the Timing Optimization Advisor under Tools.

But as I've said, I've seen large gains with these for some designs, but SOPC systems(or more exactly, the large muxes inside SOPC bridges) don't have huge gains here. I've seen users re-architect their designs and get the best results(systems where everyone talks to everyone, and this really isn't necessary, are much better if you limit your connections. I believe there are some nice things in ~SOPC 7.2 that allow you to pipeline components, which adds latency to those specific components but can increase the system speed.) Optimizing the actual SOPC system is out of my expertise, but hopefully someone else can comment. (Niosforum may help too)