Well, seeing as I have the networks tag on my name I should be feilding this question.
Quick Disclaimer: This can and may change, though HIGHLY unlikely, but this is my reasonable estimate based on current table layouts.
The cable length max you will need for most tables at the even to be comfortable is 18-20 ft. That is if you are sitting on the end of a table. If you are sitting towards the center of the room on table with seats 126-153 you will need 24-30 ft.
So yes, after all that the 30-50 is a good safe range. What you can do if you want to estimate it more closely, go vist the seating chart. The tables there are 6 ft and your cable should reach to the dead center of the row. I woiuld also estimate adding 2-4 ft. for change in height. (Since machines are on the floor and you have to move up and there could be other peoples calbes in the way.)
There are my thoughts on it, if anything changes I will be sure to let everyone know.