Having recently DM'd a Hasted, Flying, Two-Lightning Bolts per round sorcerer, I think taking out the extra spell per round is good for any but the highest magic campaigns. It was fun though, but the melee fighter only had a purpose in tight quarters or when the sorcerer was far away. (And I wasn't going to drop electricity resistance in just to balance that, not till the end anyway).
Would movement still get a boost from this Haste? (don't have the book here). I can see Haste giving a boost to movement, AC, and an extra attack or skill check per round.
I guess in thinking about it, I would maintain it as an extra partial action but go with dropping the extra spell option.