I too have both. The gold Monster is a simple switch on and go set up. The nox 800 requires a bit of a learning curve to it. More so if you are new to detecting & don’t know or understand the fundamentals of detectors. The Gold Monster is really a gold only detector where as the Nox 800 is very good at gold & also very good on coins, relics & jewelry. Usually when you get a detector that has both abilities on gold & coins etc they are usually way better at one form of detecting than the other. Usually better on the coin side but the Nox 800 is at home on both & has been real winner for Minelab. With the Nox 800 you will need to get the little 6" coil for it which is an exta. It doesn’t come with it. But is needed for in the creeks & for getting in to tight spots that gold likes to hide in. From my personal experience using both I honestly can’t split them on there ability in finding the tiniest pieces of gold.
Depth is all dependent on coil size & of course gold size that is where the Nox 800 can sneak ahead as it comes with an 11" coil & you can get another larger coil again for it. I have found tiny gold with the 11" too on the Nox. If you want a versatile detector for gold & coins etc then the Nox is the one but it has its learning curve. The GM 1000 is very at home at finding tiny gold on bedrock but so too in my opinion is the nox with the little 6" coil.
My son who lives in Aussie asked me about my thoughts on the Nox 800 & the GM 1000 & I steered him towards the nox because of its ability at being very good on gold & coins etc. He ended up getting the nox & has found gold with it over there. The Nox gives you the best of both worlds & isnt that much more than the GM1000. One other thing is that the Nox is 100% waterproof to 3 meters depth & warrantied as such but you need the waterproof headphones to go with doing that which are another extra.
JW 