Thank you for your answers. Still I'm not sold, I don't think pros and cons have been considered fairly.
Being a 1 of in a full accelerated deck means that you'll likely play this spell (any of them) with at least 3 mana in play. There are thousands of exceptions, right.
Time is everything in vintage
Well, I had heard that card advantage was everything in vintage. I think a mix of both could do, along with card quality and other aspects. Otherwise cards as preordain, standstill, thirst... would not be played. I'm not saying tempo is not important: often is crucial. But drawing an extra card for the same effect seems huge. Imagine mystical tutor for 1U that would draw the card itself. Imagine lightning bolt for 1R drawing a card. And if 1 mana was so important, forked bolt would replace fire//ice
You are right, one extra mana can mean one extra turn or even more. If you want to answer a revoker having land + mox in battlefield fire is way better: you tap in response, wait until revoker is in battlefield, and then fry it. With electrolyze, wait at least 2 turns to have 3 mana to fry it, and good luck with wastes and spheres. However in the blue matchup CA is often more important. It's all about WHEN and AGAINST WHAT you want the card.
About Ice, I think it's a cute effect, but not that much useful nowadays: they can tap bazaar in response; with MWS it can sometimes avoid an imminent threat, but you are also not playing anything this turn; against golem it's nice to avoid 5 damage, but you need often to get rid of golem; BSC is not common nowadays; griselbrand can be tapped but player is ahead with it in play; mentor is going to be fired, not iced...
I suspect that fire//ice is better overall, but I expected at least some credit for electrolyze...