WS-G5484 "Contains a Class 1 laser of 850 nm for 1000BASESX (short wavelength) applications" is the only statement I've seen on Cisco's web site about the SX GBIC and its optical source. So you can use it with OM3 MMF out to 550m no problem.
You might be confusing the SX GBIC's optical source with 100BASE-FX over multimode, which uses an LED at 1300nm wavelength. All of Cisco's optical Gigabit Ethernet GBICs use lasers.
WS-G5486 LX GBICs on OM3 MMF would also be good out to 550m. I do not know if you need mode conditioning launch patch cables anymore to work with this high-quality fiber, for runs longer than 250m. That's probably a question for the cable manufacturers (so I guess I had better ask them).
It is true that some of the 10 Gigabit Ethernet standards support using OM3 MMF out to a distance of 300m. But as far as I know, Cisco only has 10GBASE interfaces available now for SMF. I don't know if they are ever going to come out with 10GBASE interfaces that will support MMF.
So you may want to run hybrid MMF/SMF cable; or pull two sets of fiber in parallel, one MMF and the other SMF, to cover all contingencies.
If it were me, I would probably end up recommending running SMF only, and use LX GBICs for now. They will be a little more expensive than the SX ones, but the extra expense may be offset by the savings in not running MMF. What's more cost-effective depends on how many connections you need, I guess. Distance certainly wouldn't ever be be a problem, the LX GBICs are good to 10km. And if Cisco never comes out with MMF interfaces so you can run 10GBASE out to 300m, that won't affect you because the 10GBASE interfaces they sell now for SMF are good to distances measured in 10's of km.
Hope this helps.
