I have a Browning X Bolt in 300 WSM that if i remember correctly weighs in at just under 8 pounds with my scope on it (so it's not the same as your rifle, but it is lightweight in my mind). On the bench I noticed that I did not need to hold it any differently, but what I did notice was that my trigger control needed a LOT of work. It took almost an hour of dry firing to figure out how to properly pull my trigger so the gun did not move a little bit. I wasn't "jerking" the trigger but somehow I was flexing my hand or something and it was causing the gun to move a little.
My guess is that people tell you to hold the rifle different because it can help eliminate the problems with their trigger squeeze that they didn't see on their 12 pound and heavier rifles. After shooting my light rifle and perfecting my trigger squeeze I switched back to my heavy 22-250 and my groups went from 3/4 inch to 1/2 inch!
Firing from prone I also hold the rifle normal (bipod on front and off hand underneath the butt for support) and haven't had any problems. Experiment with your particular rifle and see if changing how you hold it improves your shooting.
Here is a very interesting article that I found on another thread here on this forum and while I haven't had a chance to try it out yet I want to see what it can do to my shooting.
Hold that Forend!