I have used both the 11" and the 9" x35 coils. My initial impressions are that they are both very chatty and prone to EMI compared to the HF coils (not even in same ballpark as the NOX), but the 11" is a little noisier (makes sense since it's larger). They seem to both get a little deeper than the HF, but only if EMI is low or gone. The 11" gets maybe an 1" or 2" deeper than the 9" in general. But the 11" seems to have a little slower signal reactivity (sound) than the 9". I prefer the 9", but like vferrari stated I have the 11" for covering more ground and getting a little deeper (open fields). Frequencies for the x35 are uneventful at 4, 8, 12 and 16 IMO. I have gotten the best performance and stability out of the 25kHz frequency so far. I feel like the depth at 25kHz for the 9" x35 coil is close to or better than the HF 9" round coil at 14kHz. I also haven't gotten much more depth on any kind of target using the x35 coils at 4, 8, 12 or 16 kHz than the 25kHz. I feel like it separates well at depth as well at the 25kHz compared to the lower frequencies. Do others have similar experiences?