How to set Upstream and Downstream Bandwidth in load balance router if the speed varies?

[Markos]

Hi,

I'm a Debian user and have already configured a router TL-R470T+ to 
connect with 2 providers (by PPPoE and dynamic link). And I'm using the 
TL-WR841ND V10 router only as an access point.

Now I'm in doubt as to how I will set the Upstream and Downstream 
Bandwidth for each ISP if every time I do a test (for example on 
www.speedtest.net <http://www.speedtest.net>) I find a different speed 
that can vary from 2 to 20 Mbps?

Any guidance?

Thank you,
Akvo