measuring DNA Fragments after Benzonase

[louhazosc]

Hi all,
Currently I am doing protein purification utilizing Benzonase to remove or degrade DNA in my preps. One of the standards I must meet besides total ng content is that fragments must be below 200bp.
So from each of the stages of protein purification I take a sample and do a QIAamp DNA clean up/extraction and run the samples out on a 2% agarose gel. Now of course since I use Benzonase/nuclease I get a lot of streaking with a brighter high density section in each lane.
Is there anyway I can establish what my highest bp size fragment is within the agarose gel streak or could someone recommend an alternative technique to establish what my largest fragment size would be?

Thanks