The problem with the diameter for tuning is the bigger the head the more area that must vibrate.  I've played 18 onch floor toms and have never been able to get them to sound right to me.  Now about the depth issue You need to look into the length of the sound waves you are creating.  I do not think you'll get an octobon sound but I just dont think it's gonna be the sound your looking for either..  As some one else said if your playing with logs you may be able to open them up a little by hitting them harder, but.....

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dont do it!

personaly i think they will sound unfocused, get lost in the live mix sound, sound 'muddy', will be very hard to record, and make you look like a child playing grown up drums. remember your going to have to find cases for these monsters and transport them. 

spend the money 'standard sizes' and some mics, or get into 'triggers' if your after a massive sound (effects)

just my $0.02

Rich may have come accross the best solution for you unless your looking for that "BIG" look...  But also remember WHY double bass pedals came into existance.....  So you did not have to carry the extra drum....

Until you have gigged everyday for a few weeks you will not underestand this concept.

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