In general, performance is similar. On airband, scanning the same channels, the traffic received is nearly identical. Most of the difference was picking up different traffic when two different frequencies had simultaneous keyups.
I had a couple of frequencies where a nearby pager transmitter bled over on the SDS units, but filters took care of that. So the SDS are somewhat more susceptible to adjacent frequency interference, but the also have settings to deal with that interference. My default global filter is Normal, and switching to Invert for problem freqs took care of them. So the SDS models have very similar sensitivity compared to the x36, but somewhat worse selectivity, at least without using the filter settings.
If you live right next to a pager or TV transmitter, and don't have simulcast in your area, an x36 unit might be better. But in most cases, a SDS will be just as good, and for simulcast, they're clearly better.