Rick
I'm fairly new to the Quattro also and I did the same thing you are doing now when I first got the Quattro.At first the 10.5 coil gave me some trouble( or better yet I had some trouble with, the coil is great)because it is to large to separate targets that are close together.I went to an 5 inch coil for target separation purposes and had great results.At first also if you swing that 10.5 coil much you will feel it in your arm and shoulder because that sucker is HEAVY.This passed in time as I built up strength from using it.Check out the Sun Ray and Excellerator 5" coils on the market for the Quattro.These coils are not so heavy obviously and have great target separation capabilities that helped me in getting familiar with the Quattro.I opted out of the 8" for now because I wanted a range of coils 5" 10" and 15" for a wide range of detecting purposes dictated by conditions.I hunt in some really trashy areas(5"coil)some not so trashy areas(10.5 coil) and some beach area 15" WOT.This does not always hold true but it was a good start and I can experiment with the other coils at the different sites to gain knowledge on what to expect out of them.In the future (soon I hope) I'm going to go with the JOEY Coil(5X10)for some tighter areas that I can't get the 10.5(round) coil into.
This will give you some food for thought for now. Get back with us on what you decide and how it preforms.At first I learn something new almost daily about the Quattro from either using various coils or reading post here. There is some really good stuff from some really experienced people here on the site.I take full advantage of the Info here and it has really shortened the learning curve for me on the Quattro.
Good Luck and Good Hunting
Warriorwon