Are you looking in the RT core rulebook, Into the Storm, Battlefleet Koronus, Edge of the Abyss, Stars of Inequity, Hostile Aquisitions or the Navis Primer? Outside of Soul Reaver I don't own any of the adventures, but I do own every other book and several engine types increase the speed of the vessel, particularly on the Viper scout sloop and Sprint Traders.
Best Quality Engines or anything that gives you the modified drive archeotech upgrade (Planetbound for Millenia/Reliquary of Mars) can also push the speed up.
Either of those also let you take Augmented Retro Thrusters, which increase maneuverability.
The other thing is that the Defiant, unlike other CL carriers, has a Str 2 LB per side as opposed to Str 1. (Weirdly, both BFG and RT GENERALLY have the same Str for weapons.)
A little quick work and...
DEFIANT Class Light Cruiser
NAME Lenore
TURRET RATING 3
SHIELDS Single Void Shield [C:BEST]
ARMOUR 20
SPEED 7
HULL INTEGRITY 60
MANOEUVRABILITY 17
DETECTION 20
SPACE AVAILABLE 63
POWER AVAILABLE: 66
SPACE Left Over 0
POWER USED 64
Skill Test Modifiers
Navigation/Warp +10, Social +20, Investigation +10, Intimidate (Social) +10 w/Active Hymn-Casters, CMD/Hit&Run +20, CMD/Boarding Action +20, CMD/Hit&Run (Def) +25, CMD/Boarding Action (Def) +25, Command (Attack Craft ) +5
Crew Disposition: Fanatical
Crew Max 100%
Crew Quality Competent (35)
Morale Max 108% (Current) 100%
Normal Operations (Morale)
Attack Craft Rating +2
Achievement Bonuses: Trade + 200 Crime + 125 Creed + 100 Military + 100 Explore + 150
Essential Components
Jovian Pattern Class 3 Drive [Modified/Archeotech], Strelov 2 Warp Engine (CL,C) [C:BEST], Warpsbane Hull, Flight Command Bridge (CL,C,CB,CG; Tests to ready new squadrons automatically pass) [C:BEST], M-1.r Life Sustainer (+1 Morale Loss) [C:BEST], M-201b Auger Array [C:BEST], Clan-Kin Quarters (All morale loss reduced by 1, minimum 1) [C:BEST]
Supplemental Components
Compartmentalized Cargo Hold, Barracks, Augmented Retro Thrusters, Extended Supply Vaults (Extended Repairs add 1 additional HI point), Temple Shrine to the God Emperor, Librarium Vault, Trophy Room, Observation Dome, Broad-Band Hymn-Casters (Enemy must make Diff. -10 Tech-Use Test for Vox/Comms) (External, 30VU), Empyrean Mantle (When 'Silent Running' it is 2 Degrees HARDER to detect this Vessel)(External), Crew Improvements: Best (+3 Morale, +5 Quality), Ostentatious Displays of Wealth (Best Quality), Starchart Collection (-1d5+5Days Warp Travel Time, Min. 1 day), Pilot's Chamber, Small Craft Repair Deck, Flak Turrets (-10 Detection Penalty when in use), Power Ram (External, +1d10 Ramming Damage),
Background Package
Planetbound for Millennia (+10 Mvr w/in 5VU of a planet)
Weapons
Godsbane Lance [Strength: 1, Damage:1d10+2, Crit Rating: 3, Range: 12] Location:PROW
Jovian Pattern Landing Bay [Strength: 2, Damage:x+x, Crit Rating: --, Range: ] Location:STARBOARD
Jovian Pattern Landing Bay [Strength: 2, Damage:x+x, Crit Rating: --, Range: ] Location:PORT
I've read stories about people who fielded a fleet soley of Endeavour's, Endurances and 'bfg-forbid' Defiants.
They made such a visual impact (lots of models with high turnrate) that the enemy fleet lost easily.
I've heard of this too, but never seen it. They usually die to the first Eldar/Chaos/Necrons fleet they meet. They do pretty well against Tau though.