And don't forget my DRT-5FC. 
Well, I still haven't apparently four years later. I got this in my head today and decided to flesh it out with some fluff.
DRT-5FC DARTMass: 25 tons
Chassis: CMW Model D-4 EndoSteel
Power Plant: Vlar 300 XL
Cruising Speed: 130 kph
Maximum Speed: 194 kph
Jump Jets: None
Jump Capacity: None
Armor: Lexington Ltd. High Grade Ferro-Fibrous
Armament: 3 Defiance B3M Medium Lasers
Manufacturer: Coventry Metal Works
Primary Factory: Coventry
Communications System: Cyclops 14
Targeting and Tracking System: Cyclops Multi-Tasker 10
Overview:
Some Lyran technophiles weren’t satisfied with the 4FC insisting that the Dart was capable of so much more. While many Steiner traditionalists viewed this as a wasteful effort there were a few nobles who could afford a luxury upgrade package and with the entire FedCom market available Coventry Metal Works authorized such a limited edition. Sales and early performance reviews have justified the company’s decision despite some in the LCAF state command who continue to see this model as an unnecessary extravagance.
Capabilities:
Working off the improved DRT-4FC design engineers simply replaced the heavier VOX 225 Engine with the more expensive but readily available Vlar 300 XL. This high-tech power plant imported for another Coventry Metal Works’ product required little other changes to incorporate into the Dart. The three-ton gyroscope onboard remained quite capable of balancing that bulkier but higher rated power plant which increased speed to a maximum of 194 kph. This allows the ‘Mech to outpace the Clan Dasher on average without a MASC and even match the impressive base movement of the new LCT-4M Locust. Allocating the half-ton of design weight left over from this engine swap towards armor allowed designers to maximize protection. Five tons of Lexington Limited High-Grade Ferro-Fibrous now cover even the limbs of the Dart which had previously been under armored. Detractors enjoy pointing out the vulnerability of the Extra Light (XL) Engine opposed to their standard Fusion counterparts but no one can deny the impressive capabilities of this fully optimized variant. The only downside to some technophiles is the decision to retain the original ten Single Heat Sinks of the basic Dart design. They insist that the current weapon package combined with maximum movement will tax the cooling system with continued use and future upgrades could necessitate Double Heat Sinks which the 300 XL can easily incorporate. Technicians point out that simply holding fire with one of the three Defiance B3M Medium Lasers every fourth round would result in a heat neutral firing pattern. While true some Mechwarriors insist that they need every advantage to counter their adversaries on the battlefield and no expense should be spared. These upgrades on the lostech EndoSteel frame aren’t cheap however and with a final price which doubles the original DRT-3S design executives were happy to appease critics with some cost savings.
Deployment:
The first orders for the 5FC were routed specifically for the new Bolan Scouts of the LCAF, the elite Davion Light Guards of the AFFS, and the 4th Deneb Light Cavalry of the AFFC. Considered the premier Light Mech units of the respective militaries of the Federated Commonwealth it was up to them to evaluate it initially. As initial reviews were going on sales were also authorized to the Kell Hounds and Eridani Light Horse as trusted mercenary commands with long ties the Steiner-Davions for ‘additional independent analyses’. In all cases the reviews were highly favorable and further orders went out to the rest of the Deneb Light Cavalry, the recently expanded Davion Armored Cavalry, and the Robinson Rangers. Priority was given to those commands serving along the Clan front and there appears to be no lack of future demand. Currently one in every four Darts made by Coventry Metal Works is a 5FC with the original 3S being completely discontinued in order to make room for production.
Perhaps the most flamboyant unit fielding the new Darts is the so-called Red Barons of the Bolan Scouts. Charlie Company of the 3rd Battalion as they are officially known employs an entire company of Darts in service with the LCAF. The Scouts are a new light unit in House Steiner service with dreams of becoming the next Tamar Hussars or the Stealths in the future and the Barons happen to be three young Lance Commanders. Wealthy nobles they are the patrons of this unit which knows they have fast competition LCT-4M and Clan Dasher. Hard drinkers and dart players when not fighting they have already earned quite a reputation around the Commonwealth for their early exploits.
Variant:
As with the 4FC, one of the most common variants is the replacement of the head mounted Medium Laser with Targeting Acquisition Gear or TAG. This allows the ultra-fast Light 'Mech to serve as a spotter for AFFC artillery units equipped with Arrow IV Homing Missiles. Thanks to its inherent high-speed capabilities this 'Tagging Dart' is well suited to serve as more of an observer rather than a direct combatant for the Federated Commonwealth.
Type: Dart
Technology Base: Inner Sphere - Level 2
Tonnage: 25
Equipment Mass
Internal Structure: EndoSteel 1.5
Engine: 300 XL 9.5
Walking MP: 12
Running MP: 18
Jumping MP: 0 0
Heat Sinks: 10 0
Gyro: 3
Cockpit: 3
Armor Factor: 89 5
Internal Structure Armor Value
Head 3 9
Center Torso 8 12 / 4
R/L Torso 6 10 / 2
R/L Arm 4 8
R/L Leg 6 12
Weapons and Ammo Location Critical Tonnage
Medium Laser Head 1 1
Medium Laser Center Torso 1 1
Medium Laser Center Torso 1 1
Cost = 4,423,750 C-bills
(compared to the 4FC which is 2,380,000 C-bills or the 3S which was 2,183,750 C-bills)
