SONAR is not intensive for video at all, so even a moderate card for graphics is fine. Ironically even high-end 3D cards don't "excel" at 2D either... they are geared for 3D, not 2D, so a heavy-handed 3D card still isn't going to gain much in the 2D realm (and unnecessary).
Bottom line, if the performance isn't obviously bad, looking at benchmarking software can just get folks focused on "non-practical application." The SSD on the Program/OS drive is #1 priority (and most benefit), and seems you have that. Max-throughput on a data drive is rarely going to be achieved and really unnecessary - sort of like a car that top-ends at 240mph... where are you going to top-end it at? Moving the entire contents from one to the other would be about it.
With that said, have you tested out "real world" performance running some projects you are familiar with? The X3 Demo project I have found useful to try various things out (especially good for setting buffers on audio interfaces). Streaming situations or intense orchestral libraries would be the best test, but I have never done either of these.