Thanks everyone for your contribution. I don't think enchanted items alone will work only so far. Sure an armour or a block can help, but I think infight counterspells can really add to a high power game.
As a houserule, I would do it like this:
Without the lore roll to determine how much power the spell was cast at, so the counterspeller is flying blind. He makes a counterspell evocation at a power he choses beforehand, done by the standard evocation rules, including mental stress. If he is not able to match the power of the spell with the power of his counterspell, the only thing he achieves is to lower the weapon rating of the spell, it still hits with the full discipline roll made plus the remaining power. If on the other hand the counterspeller is above the power of the incoming spell, he gets an extra stress per shift of power above the incoming spell, reflecting the power that is summoned yet unused . Plus, the counterspeller has to have his action waiting for a spell to counter, it is not a defence action.
So in my example from above:
Weapon:7
Discipline Roll: 10
The defending sorcerer tries to counter the attack. He doesn't think his opponent would go all in in the first round, so a counterspell:5 should do. He rolls a 6 on his discipline roll, so he can easily apply his will to the incoming attack. Unfortunately that only brings the powerlevel of the spell to a 2, which is still enough to inflict 12 physical stress combined with the shifts from the attack. As an evocation, the counterspell inflicts 1 base stress, because it is at the conviction of 5 (bonus from foci would apply) of the counterspelling sorcerer.
If he had gone with a counterspell:8 instead, it would have looked like this:
assuming he succeeds in his discipline roll, he overshot his counterspell by 1. He rips the incoming attack right out of existence, but now he has to deal with the backlash. First, he will get 1 base stress plus 3 for each level of power above his conviction. And 1 additional stress for the 1 power his counterspell is above the incoming attack. This results in 5 mental stress. Not cancelling the stress out to zero, but this is a hell of a lot better than in the example above.
You can wear yourself out by this quicker than if you would sling out spells yourself, but I think it is a good option. Maybe another rule to add 2 shifts to not cancel out a spell but redirect it. The rules above would still apply, so if you have an power 5 spell incoming, you would have to at least put 7 shifts into the spell to redirect it. Anything above that gives an extra stress as a standard counterspell would, but it does not increase the spells power. If the counterpower (power - 2 shifts for redirecting) is below the attacking spell the attackpower is just decreased as above, nothing is redirected. The redirection attempt has to be announced before the counterspell is cast.
And last but not least, I might go with the penalty for not knowing an evocation element, but I don't know if that really is necessary.
Oh and one absolutely last thought: the sight should cancel out the "flying blind" disadvantage, making it possible for the wizard to assess the power of the spell by a Lore roll. I was first thinking of just having him know the spells power without a roll if he activates the sight, but that would be too easy. Plus, that way the sight is not such a major advantage, so any wizard would still think twice about opening it up in a combat situation.
I would have to test this, but I like it so far.
