you can make the same power with either 4s or 8s. just going high voltage means you drawl less amps to make the same power. i've built two trucks that'll both flip from a stand still like the mgt on 4s does. its expensive to get everything you need, but worth it once its done. my first conversion to high powered brushless was an emaxx, and that was the worse truck to do it with. i sank so much money into it just to get it to hold up to the power. considering you already have an mgt, your cost won't be so much. if you want to know how to do it cheap, i have some solutions for you. it doesn't have to cost $700 to have something fast and reliable.

heres some vids of my cars.
emaxx

http://www.youtube.com/watch?v=Mlc3gsyTQFI

1/8th onroad

http://www.youtube.com/watch?v=AzPgSRjPY8g

lightning stadium 10

http://s39.photobucket.com/albums/e1...essLS10004.flv