I've been through a lot of the same stuff....
I have a Giant XTC SE2, came with a Duke 80mm air. Got lucky and a buddy lent me his dying Marz Atom 80 coil. Coil made the ride SOOOOOO much better, but as expected the fork died, so I had to replace it again.
yada yada yada
I ended up taking the Marz MXComp (I'm not sure but I think the MX Comp and MX Pro are two different forks, ie: mutually exclusive?) with ETA and 105mm off my Enduro and put it on my Giant. The steering is ever so slightly slower and less responsive. I almost never notice it, except sometimes on really fast, wide flowy turns I have to work harder to not go wide.
All in all, I think the move to 105 is a good one, and I don't regret it.
On the other hand, I think the MXC is a cheaper fork than the atom 80, and I will NEVER ever go to an inexpensive air fork again. This is of course related to preference and riding style, so it may or may not relate to you, but I would trade the small bump compliance and suppleness of a decent 80mm coil for the extra travel of a 100-105 in a second. The Atom 80 was a perfect fork for riding aggessive XC on my HT. On the other hand, it takes a pretty decent bump to get the MXC going, and it is just more harsh than a decent coil shock, hands down.
FWIW, I went from 105-130 on my Enduro and LOVE it, I'm using a Fox Vanilla 125r there.
One peice of advice: If you are really concerned, you can look at the Fox, because it is internally adjustable, and if you don't like the 100 setting, you can go back to 80. There are also the Rockshocks UTURN forks. While I am not a big fan or RS, I think the Duke and the Psylo get "pretty good" ratings if you are not too heavy. You can check the reviews and decide for yourself, but both of those are under $200 new.