40Mbps Internet limited to around 20Mbps

So, not too long ago I upgraded my internet connection to the 40mbps. but my computer is not achieving this speed. the best ive seen was 25mbps, wired directly to modem with ethernet cable. But i do know that the the speed is there with the service, because the cable guy ran a test with his laptop and he got 38mbps wired and wireless. So something with my computer seems to be limiting my speed. just dont know what. I have disable all programs that would slow my connection down.. so that is not the issue here. anybody have any ideas as to how to fix this problem?
The cable tech mentioned something about me running win 7 ultimate on my computer and that my computer wasnt designed for win 7, but for win vista. he said that could be part of the problem. is there any truth to that?
 
I just wanted to send out an update on this problem.. this problem is solved.. it was Avast web shield that was slowing down my internet connection.
 
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