The sample rate at 27MHz is 40MS/s I/Q.
Yes, you are correct about the step size in the playback box.
Another alternative is to use the spectrum settings to control which part of the capture is shown in the spectrum plot. If you set the offset to two different values and then calculate freq/time you could get a sweep rate. We are making improvements to this as well in the next release which should simply this process even more.
Regards
