I just managed to pass "Server Crash" on my first try after getting through those turrets and getting into the catacombs. I also managed to use that special spot when holding off on the DSM and downloading the files along with taking down the two shields guys who are hard to hit and the Juggernaut with one flash and nearly a clip of LMG ammo with the headshot.
Smacktown: It was a complete nightmare because you cannot take cover in the beginning at the helicopter because you are stuck outside trying to murder the dozens of troops that keep coming. Especially after destroying the smack, you don't know if the enemies will just keep coming the way the are.
Not looking forward to the stock market one. Having to get the codes and then having to upload all 9,000 files is a severe pain that the enemies keep spawning and one screw up can easily end in failure.