Well.. upon further review, I think my modem tweaking was just a coincidence. Tonight I seem to get more or less the same results with the default Windows settings vs the tweaked ones. Think I got too excited. In my haste, I neglected to change back to the default settings to see if the tests went back down, and then change back to the tweaked settings to see if they sped back up again. Dumb on my part… 
I was so impressed by this I just had to post about it. I decided on a whim to try out the Tweak Test at DSL Reports. I followed their advice and used the DRTCP tool to change my RWIN setting to 135000, Window Scaling to Yes, and Timestamp to No. I then ran some speedtests after rebooting my system and noticed a large improvement! 
I arrived at my RWIN setting by taking (60ms x 1.5 * 12000) / 8 = 13500, where 60ms = my average latency or ping time to most sites and 12000 = my download speed since I’m on Cox Communications’ 12-15Mbps/1000kbps speed plan. Following is a screenshot of the DRTCP tool:
Here are some before and after speedtests:
Before:
After:
That’s quite an improvement on my download speeds! Woohoo! 
