How to tell if you have enough distortion ? (FUCK THIS LOW GAIN)

Haha, I think you could get by with more amp distortion, I generally don't use a whole lot, just enough to hear it crush on palm mutes, but not enough to fuzz it all to fuck and back. There was an old Sturgis thread with something along the lines of "Crank it up until it's too much and sounds like ass, then back off a hair." I take that to heart.
 
This really depends on what kind of a tone you want. If you want incredibly focused, dynamic and attacky sound with no fuzzy top nor crushing bottom (think some Arsis albums) then you want really tiny amounts of distortion. If you want an incredibly fuzzy top end and crushing bottom as well as a really compressed tone (think: most death metal, also Gojira's last three albums) then put insane amounts of gain, then back it off till you start hearing pick attack come through the 500-2000 range.
 
start palm muting as you turn the gain knob and when you hear a movement to the tone back it a little bit. done. that's enough.
 
I guess you can have too much of the wrong kind of "gain"

I like the track though (listened to it twice)
 
I usually aim for a balance where I start to get a bit of chunk when chugging away, but still hear all the notes when playing a chord. At first you may have to reamp a couple of times to see how it builds up, but after a while you get a better feel for it.
 
I always tend to go with this when dialing in a tone (getting a great tone already at the source ofcourse): Let the player, or yourself (whatever situation it is) play to the drums that are tracked/programmed already and just start by listening what the tone needs (less/more gain). As Mentioned above already, if it gets "too much" just back it off a bit.
It basically just comes down to trying out alot and doing mistakes, and learning from them.
Hope this helps you out!