Yeah, could be Wine that's limiting the speed, I don't know. Haven't really done any 16X-plus burning in Linux.
Some additional info: it's possible to get the capture buttons back by using unmanaged windows (also requires gdiplus.dll to save the .png). Create Disc works for Data Disc, "Burn Image" gives an error. "CPU Usage" doesn't work either and "Simulate" seems to have left burn traces on this disc, it's not empty (but not burned readably either) after the test.
The second screenshot was done in Windows for comparison. Pretty consistent.