unganged is best for quad-cores and for multi-threaded applications. ganged is best for single-threads that use a lot of memory. to my knowledge, Sonar does a bit of both. i don't think i'll will matter much. i would probably stay with unganged as most apps are multi-threaded these days.
but, the difference is very small either way. and it's about memory bandwidth which has very little to do with audio engine performance. the biggest thing for Sonar is CPU (the floating-point benchmarks).
even for gaming where you have a lot of texture swapping cases where memory bandwidth matters, the benchmarks i've seen where like 0.1 percent different. there are many other factors and settings to worry about that will have a more dramatic effect on performance.