How about shooting HDV mode for this? When I think "seminar" I usually run into poor lighting, bland backdrop, typically not the kind of thing that you need top quality for. Obviously you want to deliver the best product possible, but I'm thinking HDV would be capable of delivering just fine and with a lower bitrate.
I haven't had to do any seminars since we ditched our SD gear, but I've already tested our old Firestore with the EX cameras. It'll accept HDV via Firewire, so I plan to just do that so I don't have to worry about card capacity.
I shoot for a government dept in Canberra Australia. We do a lot of seminars in addition to regular field work using three x EX3 kits and one x Z1 . When doing day-long seminars we shoot direct to a Sony PHU60K accessory hard disk unit. We use the SP 1080/50i setting giving us about 300 minutes of recording. This format is quite suitable in terms of reproduction given that many of the rooms we work in are not properly lit for high-end video outcomes. We attempt to light the subjects as best as possible, but once they start walking around - especially in front of a Power Point presentation on screen - then the whole shoot turns to crap. Good luck.