Yikes. Those memory resources on the last level. Too many explosions and zombies at crucial points when you need to maneuver the vehicle. The game gets slowed down.
OK guys, Lightning is by far the worst of the weapons. Guns are not too bad (mediocre). Missiles are where it's at. Also, multiple magnet or speed panels DO stack. I use 4 fully upgraded magnets and one speed panel. Make the rest missiles or missile/gun combo and you can sit in the middle of the screen and farm cash.
On the final level against the Brits. Just had a few green jackets that hit my blockhouse from the intersection on the three starter arrows. Like four squares in front of the choke point. Also, ALL French discounts are broken. Don't know about the British ones yet.