As far as cheats, tips, tricks and such, I use gamefaqs. For the 6 star acheivement, I used an armored truck and drove through the barricade towards the begining of the game (because the bridges are blocking you into one area). Automatic 6 stars and at the end of the bridge, I got poly-clipped and landed on the other shore. Just hid for a while and fought off the randoms. Got the acheivement REAL fast.