Same Broadband speed test, slower on Safari than on Chrome

Hi,

I have MackBook Pro (mid-2010) on 10.6.8 (snow leopard) with Safari 5.1.10 and Google Chrome 34.0. I use ATT Uverse Max Plus (up to 18Mbp download, 1.5Mbp upload).

I tested the speed using www.speakeasy.net the other day with these 2 browsers and got wildly different results.

With Safari, I consistently got 16Mbp or less on download. But with Chrome, I got more than 18Mbp dl most of the time. Similar speed on upload for both.

I have similar extensions for both browsers (Smartvideo for Youtube, iTube Studio and Youtube download). Beside those extensions, my Safari has Google translate but there are more extensions actually on Chrome (Hangouts, Embed WMPlayer inline, Divx Plus Web Player, Video 5).

I disabled Google translate and Youtube download on Safari. The speed got up a bit to 18Mbp max.

I even tried deleting the Cache.db for Safari, repairing disk permissions, and PRAM reset. No change.

Can someone explain to me why this happens?

Can someone tell me if there is an inherent problem with Safari, or I need tweak Safari more (e.g., disabling more extensions)?

Thanks,

Gary Leung