When troubleshooting your internet connection, a good place to start is to run speed tests on ethernet vs. wireless. The comparison will help determine if wireless is providing the maximum possible connection. I also see you have a number of different systems which you can test. The comparison between the G75 results and results from another laptop will be useful in identifying problems that may be specific to one laptop.
As you test wireless connectivity,
http://www6.nohold.net/Cisco2/GetArticle.aspx?docid=266cc1c7b97c458fb04c2da21f985828_List_of_Common_... discusses potential issues with Linksys Wireless-N routers. I don't know what brand of router you have, but many of the recommendations in this article will apply to most routers.
For some additional background information,
http://www.wiredrive.com/knowledge-base/troubleshooting/factors-that-affect-uploading-and-downloadin... discusses factors that affect upload and download speed. It was written for a specific product called "Wiredrive", but again, the explanations of what factors cause speeds to vary apply to any download over an internet connection.
It's important to realize internet connection speeds will vary on every system, even when completely optimized.DPC Latency can also rob you system of performance on a number of fronts, one of which is download speed. McAfee Antivirus has caused such issues on G75 systems. See
http://rog.asus.com/forum/showthread.php?14960-G75VW-random-audio-and-graphics-spike/page2 for additional information on this issue.
DPC Latency Checker (
http://www.thesycon.de/deu/latency_check.shtml) is a good tool to use for troubleshooting latency issues. On the download page, there is also a good guide with screenshots that discusses how to use the tool.
The Atheros Wireless cards that ship with G Series systems are budget quality. In addition, some of the earlier Atheros drivers have had high DPC Latency issues that resulted in many problems on G74SX systems. I have read of one report where the user indicates uninstalling the Atheros driver that ships with the G75 reduces latency. That will be useful for you to confirm.
To achieve better wireless performance, some G Series laptop users have upgraded their WiFi cards to Intel 6250 (if you want to retain Bluetooth functionality on a WiFi card) or the Intel 6300 for maximum speed. Be aware that replacing the G75 WiFi card is more involved than on a G74, requiring disassembly that may void your ASUS Warranty.
Lastly, there are a lot of ASUS Bloatware programs running on a G75, running a lot of processes that use resources on the system. Choosing to have most of them NOT load at startup in the "Startup" tab of MSCONFIG.EXE may help increase performance on the ASUS Factory OS installation. Uninstalling some of these programs from "Control Panel - Uninstall a program" may also help performance. Be aware that some of the ASUS programs, such as "Instant On" are heavily intertwined with the OS and can actually cause problems when uninstalled (see
http://rog.asus.com/forum/showthread.php?17721-Instant-on-thing-is-pissing-me-off).
The best way of eliminating the performance issues associated with ASUS Bloatware is to perform a clean Windows 7 installation. The only ASUS program really necessary is the ASUS ATK Package to control Function key functionality. If there are ASUS programs you find useful (I like Ai Charger Plus to charge my cell phone, even when the laptop is shut down), you can always download and install them from the ASUS web site or your Drivers and Applications CD.
G74SX-A1 - stock hardware - BIOS 202 - 2nd Monitor VISIO VF551XVT