Our group is considering changing the rule that states that the force of the spell limits the total hits on the spellcasting test, to instead only limiting the net hits instead. This is mostly for combat spells, really. We'd already been doing it like that for almost a year now, and we only noticed that we had originally misread the rule before one of our sessions last month. We tried playing a session through with the actual rule, but it seemed a bit stupid to us that it doesn't matter how many hits you roll, the damage is completely reliant on how many hits they get on there resist test. 1 hit on the resist test automatically reduces the damage by 1, no questions asked since the hits used to match them on the opposed test and to increase the damage share the same cap. Hell, the change really only comes into effect when you roll more hits than the force of the spell, and since our mage is a 3rd grade initiate with 8 magic, he's usually tossing out force 8 spells and doesn't often roll more than 7 or 8 hits. But it makes more sense to us, since it rewards him for making good rolls, and the damage is still meh when he rolls poorly.
Opinions?
In my opinion that can make a mage REALLY powerful. If you have a mage with Spellcasting 6 + Magic 8 + various focus = 5, then he's rolling 19 Dice for that attack. If you're casting a force 8 spell, normally you'll be limited to only scoring 8 hits, but if you guys don't limit that, your mage can roll 19 successes and then he's doing 19 hits. So then, the opposed character rolls a willpower + counterspelling (maybe 7 dice) and lets say he rolls 7 successes which is the most they're ever going to make. This would now net you 12 hits, but since you're limited by force he's netting 8 hits. So 8 hits + 8 force = 16 DV. Depending on the type of spell you're casting, this could be a one hit kill. Maybe you like it that way?
But if you limit their TOTAL hits to the Force of the spell, then they're only scoring 8 total hits. So if the opposed character rolls the same seven, you're only getting a net hit of 1, which gives you a DV of 9. DV 9 is going to be much more manageable for the enemy to soak and won't be any kind of instant kill.
Effect:
With your method: a powerful mage can keep casting spells at force 8 and crippling their enemies with a force 8 spell. Reducing the drain from a force 8 is easy, I doubt your mage ever suffers drain at force 8, its almost negligible.
With the book method: since casting a spell at force 8 is only going to get a small DV through, it forces the caster to cast at higher forces. They can cast at Magic x2, so your mage could cast up to Force 16 but why would he? With the books method you'd HAVE to cast at Force 16, or even Overcasting into Force 18 or 20 if you really want to demolish an enemy. Reducing the drain from a Force 16 spell is going to be tough and the mage might take a stun hit or two. (or some physical damage if they're overcasting)
Sorry for the long post but if you want to play a game with super powerful mages that don't suffer drain, your way is fine. Some people probably prefer that and it might be easier for new players (especially new mages). But the rule in the book is meant to balance a spellcaster. if they want to do serious damage, then they have a very serious threat of suffering drain.