Desperado gets a skill called Strength that increases their gun and bow damage by around 25% (I believe, might be 20% World Of Warcraft Gold or something). This is a much bigger increase than it sounds with how defense works, and this damage boost is BEFORE defense is calculated into damage done.
Then at level 40 you can choose Hidden Soldier. Now is where you chew through things. There is both Eagle Cruiser, which is a rapid firing (with each shot doing less than normal damage [cosmetic only]) shot that deals good damage.
Then is the skill that really makes Hidden Soldier excels: Quick Attack. This skill reduces the recharge time of your skills so you can keep doing attack skills more, and attack skills do MUCH more damage than normal shots.
You can also pick Sentinel. Frankly, I like Hidden Soldier way more.
Sentinel your other level 40 choice, and is decent. There is Scamper, Divine, and Mental Assault. Scamper is like it sounds, it's to get away. Your evasion and attack is lowered so this defiantly isn't so you can run around faster during combat.