I got the 1gb iceq4 4850 a month ago and have been pleased so far. i needed 1gb for GTA4, but i think 1gb will become standard during the lifetime of your card so you might as well get it so you don't have to upgrade sooner than you would like. Only problem I have with the card is that it makes a high pitched whine when my games load up, but not when I am playing them and actually using the card. Not a big deal, but strange anyways.
Lastly, I don't even think you should look at a 4850 unless you are constrained by a psu. If you have a psu less than 500W, then the 4850 is your best bet. But if you have a higher wattage psu there is no reason not to get a 4870. It costs a little more, but it will keep your computer running the top games for an extra 6-12 months longer than the 4850.
It might seem like I keep jumping you up levels in price to the 4870 but it is really worth it in the long run. Yeah that 4770 might be $110, but you will have to upgrade much sooner and in the meantime you will get worse performance. Spend the extra $90 and it will pay for itself (of course assuming you have a capable psu).
In the short term you can justify it that one friday night out at the bar costs $100. So just stay in one friday and you will have a far superior card to the next 2 years.