I have a client that is using Cisco switches with gigabit fiber connectors. They want to install OM3 50 micron fiber to be able to change to 10 gig switches in the future. My question is will the current switches work on OM3 multimode or do they need to be running VCSEL.

I think it will be fine. But I'd really hate to find out I'm wrong after the OM3 is installed and terminated.