Cropped v FF for weddings starting out

Not sure if this is the right forum but here goes.....

Will be starting off in wedding photography next year and will be investing in some new kit to do the job. Second shooter initially.

I do some photography for our clients through my day job in a new media firm and I'm confident I can take those skills to the wedding arena. I did a course with a pro shooter and have met and chatted to a few more experienced photographers to set me on the way.

I have been using Olympus bodies with some hired HG glass but I feel I need to look elsewhere to get better low light performance and clean high ISO.

So Canon is my preferred choice as is menu system seems similar to Olympus and after handling a few Canon bodies I like the feel of them over the Nikon offerings.

So my question is what are peoples experience if any of shooting weddings on cropped bodies? I have been looking at getting the 60D and maybe the Sigma 17-50 f2.8 but I have that nagging feeling that i might be left wanting for better ISO capability especially during the ceremony in the church.

So might I be better served with say a second hand 5D Mk1 or should I sit tight, wait for the 5D Mk3 next year and get the Mk2 at a bargin price?

Just not sure which way to turn, and help will be greatly appreciated for a wedding photographer newbie!