First of all you are unlikely to notice any difference with web page loading once you go above 2 megs, the load speed change will be imperceptable. You will be governed more by the strain on the site server than anything else.
The real benefit of max is the upload and download speeds, try this site click here (it might be busy) as a check, testers come up with all sorts of different answers for many reasons.
Can I assume your download speed is from experience of actually downloading as opposed to a speedtester? If it is then ring Zen or use their excellent speak to helpdesk facility where you can have a real time messaging exchange.