This is going to come off as rude, but I don't know how else to word it; the rumor stated within the next 18 months. If you can seriously put off a purchase for 18 months, then you don't NEED either of these lenses. Why don't you buy the extremely affordable 24-105L F4 IS lens? A year and a half is far too long for any professional or semi-professional to go without a normal lens. Sell it in a year or two at a minimal loss (Hey, you got to use it for 2 years, right?) and then make your decision. You may decide the cheaper 24-105 is all you actually need, especially if you are just a hobbyist. Like neuro said, it's silly to make purchasing decisions based on rumors, and even sillier when the rumor is 18 months away.