A friend wants me to do a colour photo of a 'babbling brook" that will be enlarged to 2' x 6' for a poster for her shop window. I can shoot from 6x7 to 8x10 (including 5x7 although I can't seem to find any 5x7 colour film).

Which format would you use for such an application? Negative or reversal? Will 4x5 or even 6x7 do the job and is 8x10 overkill (it certainly is more expensive to scan)?