Cheiromancer
Adventurer
I'd need to take a generic fighter and some generic opponents, and run some mock combats. But the kind of thing I would be looking for is: if a 10th level fighter does 10 hp damage per hit against a CR 10 creature with 100 hp, that's 10 hits to get the 750 xp. So each blow in effect is worth 75 xp. If the +3 weapon were instead +3 to damage, it takes 8 blows to get the 750 xp, so each blow is worth about 94 xp. So, from a blow/xp ratio, the bonus should be at least 20 xp or a +3 weapon is more efficient as an extractor of xp.
Actually, it would be more than that. With +3 to hit, you'd land successful blows much more often. It might take you 15 rounds to make 10 successful attacks instead of 20. That's 12 rounds to make 8 successful attacks. So a +3 weapon would give you 750 xp over 12 rounds, instead of over 20 rounds. That's 63 xp per round as compared to 38 xp per round. To balance it a soulfire weapon would have to do at least 25 xp/hit.
I'm just pulling numbers out of the air. They are probably off by at least a factor of 2. But my gut feeling is that xp = CR is probably a bit low, as well.
On the other hand, there are optimal cases; a critter has moderate (5 or 10) DR and/or fast healing, but a poor BAB (or you have great AC), and not much damage per attack. You could fight it for a long time and get oodles of xp. But it could still be an earnest fight. You'd have to check out these cases too. Based on these cases, a formula of xp = CR could be on the money.
Actually, it would be more than that. With +3 to hit, you'd land successful blows much more often. It might take you 15 rounds to make 10 successful attacks instead of 20. That's 12 rounds to make 8 successful attacks. So a +3 weapon would give you 750 xp over 12 rounds, instead of over 20 rounds. That's 63 xp per round as compared to 38 xp per round. To balance it a soulfire weapon would have to do at least 25 xp/hit.
I'm just pulling numbers out of the air. They are probably off by at least a factor of 2. But my gut feeling is that xp = CR is probably a bit low, as well.
On the other hand, there are optimal cases; a critter has moderate (5 or 10) DR and/or fast healing, but a poor BAB (or you have great AC), and not much damage per attack. You could fight it for a long time and get oodles of xp. But it could still be an earnest fight. You'd have to check out these cases too. Based on these cases, a formula of xp = CR could be on the money.
