They'll both work. The difference is in the squish band. Basically, the black head (hi-torque) has a wider ring around the outside of the head (parallel to the piston crown). The silver head (lo-torque) has more volume.
The less volume that the head has, the more compression you will have. If you squish the same amount of gas into two different sized vessels, the smaller one will have more pressure. You just have to be careful how much you mill off the head. You don't want the piston to hit the head, and you don't want your compression to be high enough that you get detonation.
This picture might give you an idea what I'm talking about:
I know they aren't puch heads, but the head to the right has a larger squish band than the head to the left. Essentially, the head to the right is like the black hi-torque head and the head to the left is like the silver lo-torque head.
This might help too:
You can measure your squish by bending a piece of rosin core solder. Bend it in the shape shown in the next pic and place it on your piston. Install the head and turn the engine over. Make sure the spark plug is unhooked.
Measure the flattened part of the solder to determine your squish clearance. This can be safely brought down to 0.6-0.8mm
That should give you more torque. It might also make your engine run slightly hotter which isn't too big of a deal on a stock bike. It starts turning into a problem when you have a highly tuned engine that is already running on the hot side of things.
So yea, go for it. If it gets messed up, stock cylinders are cheap.
Oh, and I don't run any of my bikes with head gaskets. As long as your parts are flat, they should seal without a problem. I usually use a little gasket sealant to make sure everything is nice and closed up. That should give you a little torque too.
If you take too much off the head, throw a head gasket in there. No big deal.
There's even more to it and I could keep rambling, but I have a feeling that that's enough to get you started.