528mod is a milder version of the 528stock. I've never tried it, but with 7.5 you pretty much have all the motor you want. I run 205 with 9.5 and lower. Anything lower than that your throttle finger is more important with especially when traction is low. Just be careful with settings and temps. If your having success than cool. Post some settings to share.
I recomend JP Richards setup off the site. Dude is wicked fast with buggy and truck using 205.
http://www.speedpassion.net/en/escsetup.asp