Missions & Complexes

I'm assuming that the 610 is with T1 ammo? T2 will push you closer to 800 but it's not really worth the added expense as you will waste a lot of missiles on elite frigates.

610 dps with kinetic missiles, am i right? Some rats (for example, Blood Raiders) have high resistance to kinetic damage, that may be your problem.

Well, that's not the whole story. First, shooting Fury at sub-BCs, especially without GMP 4/5 and TNP 4/5, can be an exercise in frustration. Second, BSs still take a few volleys to down. This is from memory, so forgive a margin of error: Serpentis BSs usually took me ~8 volleys and Guristas BSs ~11 with similar numbers in a Nighthawk. Third, make sure you aren't overvolleying; when at range it's absolutely critical to manually stop your launchers and start shooting the next target as the last one is still blowing up if you're trying to maximize isk/hour. It's a pain, but that's what you get for using a missile ship.

I think you mean Sub-Destroyer. Most cruisers pop to a single volley. Only frigates, battleships and some battlecruisers should take more than 1 volley for a Tengu.

As for the OP, the problem sounds like a combination of fit, skills and implants. You should have no problem using 4 Ballistic Controls, with the majority of them being faction once you can afford it (purely a personal preference). With 3 CN BCS and 1 T2 my paper DPS is 754. With 4 T2 BCS, that falls to 713. Pretty significant. It's also imperative that you max out your Offensive subsystem skill if you haven't already, as well as purchasing at least +3% or better Hardwirings. Beyond this there's little else you can do to maximize your DPS aside from a 2nd account.