Different speeds wired through a Mac and PC?

I got Infinity a week ago or so and when I first had it installed I would consistently hit 70Mbits on speedtest.net.

Then after about 4 days it started slowing down to 50Mbits on my iMac. I was wondering what was up and posted as such but knew I had to wait 10 days before contacting support.

Then tonight I plugged it into a laptop and it is giving me 70Mbits again. In fact side by side I am getting 50Mbits on the mac and 73 on the laptop.

What is up? why is it showing the same speed on my laptop as I used to get on the Mac? and why is the Mac slower?

MTU? http://www.kitz.co.uk/adsl/MTU2.htm

In reply to a post by XRaySpeX:

MTU? http://www.kitz.co.uk/adsl/MTU2.htm

Are you sure? I thought it was Apple, creaming off their 20% cut!

Seriously though, yes MTU and RWIN ... no idea how the OP can tweak them on a MAC though.

Why would it be running full speed for 5 days on a mac and then slow down because of MTU and RWIN?

On later versions of Windows there is a "self tweaking" function which is claimed to set them correctly. But does it? Wondering if there is something similar on teh MAC OS and there was a line issue and it set different values? It is worth a check.

OSX has an auto tuning stack

http://www.dslreports.com/faq/3743

Try something for me as I have seen this.

1. Make sure Mail is not running.
2. Kill Safari and do the test straight after starting it again.

Does the speed return to 70?