If your client wants ProRes files for offline editing they should be 1920x1080 which he could also use for online and finishing as long as he is not doing heavy compositing with it. If there are lots of FX to do, you can do 1080 ProRes for offline and use Crimson for 1080 UC online. Of course, this all depends on what he wants he final deliverable to be.
"In Search of a Midnight Kiss" now in theaters!
Stuart Ferreyra
Timecode Multimedia
Colorist / Finisher / Consultant
Off: 310.826.9199
AIM: stuart.colorist
http://www.timecodemultimedia.com
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HD, 2K & RED Post Production for Indies at Affordable Rates"