Crysis won't max out, l4d, fallout 3 and assasins will:), well assasin's may have hiccups:P
I would also look into the 4830 since it matches the 9800 GT and can be found cheaper at times. Though if you want to b able to play it safe, either the HD 4850 or the 9800 GTX+ would be a better choice.
Thats just a general idea.
I'll assume that your monitor is 1600s resolution?