APPROVED ANSWER
replied on April 28, 2014
It's hard to say, since every form is going to be different. I would say you could make an estimate by using the F12 tools in your browser to examine the bandwidth being used.

Doing a lookup isn't going to make any difference, since Forms will be aggregating all of that data and only sending what's necessary to the client. As far as tracking the bandwidth consumption, you'll have make sure that IIS is capturing w3c logs and find a log analyzer that will show you the data, or just use Log Parser.