96mm/1.58 combo on my 414sbc works flawlessly. The 96/1.58 flows alot more than people think. A BW engineer sent me the data to prove it to me. I don't see a need to go to a bigger turbine wheel, maybe just the 1.58
The S400 96 Borg turbine is a well matched unit.. Borg doesn't make a better suited turbine for the S400. The bigger turbines actual flow less and are HEAVY.