This is a subject that has been debated at great length. Airmar sells transducers so their objectivity in describing the "dramatically better" performance of CHIRP transducers is somewhat open to question.
While perhaps not a perfect experiment, with the custom frequency presets on my TZT3s, I have done many comparisons running the fishfinder in full CHIRP mode and then running it in fixed frequency (CW) mode. Depending upon what you are trying to see, sometimes the fixed frequency does better. Using a fixed frequency like 210Hz or 180Hz can be better than the spread spectrum CHIRP for particular species or structure.
The quality of the transducer and the output power of the fishfinder is probably a more of a consideration for bottom fishing in the depths you mention. I would be skeptical that you will see a big difference between the FCV295/R109 combo and a DFF3-UHD driving the R109 in CHIRP mode. The good news is that you will have a choice if you switch to the DFF3-UHD/XL because you can still operate at fixed frequency using the custom presets and it will basically act like your FCV295. Thus you will certainly not get worse performance than with the FCV295 and there are circumstances in which you will see better performance.
If you have other reasons to go with the XL such as charting or radar capabilities, replacing the FCV295 with a DFF3-UHD could make sense. Since the R109 you have now is a CHIRP-capable transducer, you could just keep it and use it with the DFF3-UHD.