you also need to consider as with most "dumb" web browsers, they wait until all or most of the images and text have been downloaded before rendering.
what this means is you have 3 times the chance of getting one of those parts SLOWLY...and thus holding up the ENTIRE page... unless they are all lines from the same ISP.
i noticed this when i Load balenced my dsl and cable line via the Firewall + new connection state+ Nth example from the wiki. it works great!! personally i've found that you are better off using policy routing to shove your high BW guys on one line and put the rest on another.....its easier to control the high BW guys this way too.