Well, I've installed my new card and have been putting it thru it's paces all day, and I must say it has made a huge difference in SU's performance. No more sluggishness when moving the model around, shadows come on almost immediately, and everything in general seems to be snappier.
Just so you know, this was my old card ---
EVGA 01G-P3-1373-AR GeForce GTX 460 SuperClocked Video Card - 1024MB GDDR5, PCI-Express 2.0, Dual DVI, Mini HDMI, SLI, DirectX 11, Fermi w/Limited Lifetime Warranty with Registration
and my new card ---
EVGA 025-P3-1579-AR GeForce GTX 570 (Fermi) HD 2560MB 320-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
In all fairness I must say that for some time now I've suspected my old card was getting tired, so the change may in large part just be due to having a new, fresh card in place. I'll probably never know for sure, but for now I'm very happy.
Now if I could just put one of these babies in my laptop 😒