Most of my good relic finds have been made with the XLT and the 9.5 coil so I would suggest to use the same size coil with the DFX. The larger the coil the deeper the signal though in a site with lots of trash ( iron, house debris, etc. ) the smaller coils discriminate better. If you are in a "clean" field then use a wide quick swing with the 9.5 but if detecting a house site, use a smaller coil and slow down to listen for those faint good signals. Good luck! HH!
The 4X6 Eclipse is an excellent coil. I have one on my DFX and love it for trashy areas. I have picked up dimes at 7"-8" with the Eclipse. The depth reading is a little off, I was told that is because the DFX is calibrated for the 9.5" coil. The Sun-Ray probe is another must have for your DFX. Good Hunting!
I just bought the 4x6 and am looking forward to using it. The ground is starting to show a little better in this neck of the woods. I have been looking for another type pin pointer, so I'll look into the sunray also. Happy hunting, the winter blue's have been tough!