The NEW rating will be lower, they invariably supply more as they gum up a bit, that's why the ones I have cleaned always flow to new levels, older used ones tend to flow slightly better.
The comment about siemens being a better spray pattern, although banded about by a lot, I'm still waiting for evidence from back to back testing, at the end of the day it's the engine that decides if it likes the "better" pattern it may not.
Go for greys if they are free, I had greens 803's, these were on 80% duty at 300bhp, but that's real power, not fairy story.
I run greys with a slightly modded head, std cams, and a T3/34 a T3 comp housing machined out to take a T34 trim, std .48 ex housing.
My last MOT gave 0.97% CO, and 137ppm this is on a 160,000+ miles bottom end/pistons/rings.
This is NOT on closed loop, as I don't believe in it, a recent trip to Scarborough from east anglia returned 38.8 mpg, this was along the notorious A15 etc route, not A1 steady speed, used 47 litres for 402 miles.
If it's mapped correctly it will drive perfectly, I always go as low as 1000rpm in town even in 4th it pulls hard enough for town traffic dawdling, but 2K upwards is punchy.
Whatever you decide, the best money spent imo is with a decent mapping session, instead of off the shelf chip, the chip would do the job, but the mapping session could yeild so much more.
tabetha