I was looking through a lighting catalog and found two entries for D2R and D2S (typical HID capsules used on OEM assemblies, IIRC the 08 GT uses D3R). They contained info on design voltage, amps, candlepower, and lifespan. I will post them along with the specs for typical halogen capsules for comparison:

9003/H4 Low beam: 12V / 55W, 72 candlepower, 320 hours
9004 Low beam: 12.80V / 45W, 56 candlepower, 320 hours
9005 High beam: 12.80V/65W, 136 candlepower, 150 hours
9006 Low beam: 12.8V/55W, 80 candlepower, 500 hours
9007 Low beam: 12.8V/55W, 80 candlepower, 500 hours
9008/H13 Low beam (stock S197 low beam): 13.20V/68W, 87.5 candlepower, 1000 hours
9145/H10 (GT fogs): 12.8V/45W, 65 candlepower, 1000 hours
D2R Low beam: 85V/35W, 222.75 candlepower, 1500 hours
D2S Low beam: 85V/35W, 254.57 candleower, 1500 hours

Now, according to the SAE standard,
D3R Low beam: 42V/35W, ~222 candlepower, 2000 hours
The SAE standard states the same approx lumens for the reflector and shielded HID capsules (D1S = D2S = D3S = D4S in terms of lumens, lifespan, etc...) except the D3/D4 capsules use 42V instead of the 85V for the D1/D2 capsules.

The hours are in rated average lab life hours (hooking up the lamps in a vibration free controlled lab environment) and the candlepower "is the initial mean spherical candlepower emitted by the light source when the lamp is operated at design voltage."

The "R" means it is designed for a reflector assembly (Hence D3R for the 08 HIDs) and the "S" means it is designed for a projector assembly. The "2" in the D2S stands for 2nd generation discharge lighting. D3 and D4 are mercury-free. I am not sure I like the idea that the HID capsules only last 1500-2500 hours before they colorshift into pink light, because the OEM capsules are $100-$250 each, but we see that they're roughly 3 times brighter than halogens. In terms of lumens, we're looking at 1000-1300 lumens for halogens and 2800-3200 lumens for HIDs.