Speed dropped 100mb after installing DD-WRT

Hi Guys. Not sure how much you can help me with this but worth a shot.

I have a WNDR3700v4
I work for my local ISP and i am on a fibre optic (PPPoE) connection.

With the default Netgear Firmware I get 300mbps (average) here is one of my test results
http://www.speedtest.net/my-result/2860827920

I have since installed DD-WRT and now getting results around
http://www.speedtest.net/my-result/2870910728

Can anyone give me an explanation?

Thanks
Josh

Technical Infrastructure
Kcom Group