Sure. The SM200A has the ability to perform FFTs on about 500 million data points per second, but the maximum FFT size in our design is 16384. The dual channel 500 MSPS ADC is run through a FIR correction filter, a digital single sideband select filter, and then converted to 250 MSPS I/Q data (160 MHz). This can then be processed with the on-board FFT engine, or decimated further to 50 MSPS (40 MHz) and streamed to the PC, where much larger FFTs are possible.
Yes, the limitation for narrower RBWs is the USB3 speed. For FFTs on the FPGA, we impose a 120 microsecond minimum dwell time at each LO, which becomes the limiting factor, but for a 30k RBW, USB3 speed is nearly a limiting factor even for basic amplitude data.