I'm about to shoot a wedding. Groom is black and both he and his bride will be wearing white.

I had a similiar situation last year and had a problem that if I exposed for her dress, then his skin tones had way too much noise, but if I exposed enough to give low noise on his skin tones then her dress was a too over exposed to show any detail.

That was on a 1Ds, now I have a Mamiya 645/P30 should this help? I assume it has better dynamic range?

Does film have a better dynamic range? Should I shoot a few rolls of film?

Should I hire a 1DIII use its fast frame rate, exposure braketting and try some sort of HDR post production?

Forgive me, but you have a P30 yet you're asking how to expose?!

Anyway, have a read of: http://www.luminous-landscape.com/tutorial...ose-right.shtml

If the guy is very dark skinned, and you're shooting in harsh light you're going to have extreme difficulty in getting everything exposed correctly. In this instance I'd actually clip the highlights and hope that the customer prefers a 'heavenly/angelic' look

Get Fuji S5 or Fuji S3

If this is indoors and you are lighting artificially you should have no problem. If it is outdoors it is indeed a real issue. I recently shot formal outdoor shots with a similar situation with one black fellow in a group of white folks and a white dress. I shot flash outdoor to help fill in the shadows. I also used a tripod and shot without flash, three fast exposures, auto bracketed in fast succession. I explained exactly what I was doing and why. In post processing I montaged exposures to create the best possible final print. Neither a medium format or Fuji are going to give the dramatic increase in dynamic range you would need to expose for a bridal dress in direct sun with a black person's skin in the shade - or anything close to it. If you can use flash you can use strong flashes and totally overpower the sun and even the lighting out. You can do fast multiple exposures with bracketing and montage them if you're willing to spend the time. If you can even the lighting out you should be able to expose to the right and get the dress without blown highlights and still get most black skin tones reasonably well, but you do need to fully expose for the dress. The biggest issue I find is black skin in shadow with white dress in full sunlight. For that, bracketing or flash can be helpful. A huge gobo to put the entire group in the shade can work but it's often not so practical.

For something like that, fill flash or full-on lighting is your best friend. I've used a 550EX on a flash bracket with good results. But if you can set up some studio lights and fire them with a Pocket Wizard, that's even better; more power and faster recycle times. When lighting the portraits, have the main light on the side of the groom, and the fill on the bride's side, so that the white dress is getting less light than the dark skin of the groom. That will give you a bit of breathing room exposure-wise.