Here's a link to a pdf with some good info on power bars & extension cords. It is a safety bulletin for info only, but does quote some important points from legal & code documents.
http://www.esao.on.ca/downloads/info.../power_bar.pdf
If you read closely, most of use are in fact in violation of code in that we use power bars & extension cords as more or less 'permanent' solutions to run our tank gear, since neither power bars, nor extension cords are meant to be used as such. They are 'temporary' solutions for equipment that is portable.
I also don't fully agree with everything in OP's original post. With regard to the length of the cord on a power bar or the number of outlets, these factors are less important than the size(guage) of the wire in the cord & the quality of the outlets. The more outlets on a power bar, the greater the temptation to overload it with too many doo dads. A 3 foot cord of 12 ga wire is much safer to use than a 6 foot cord of 16 ga wire due to the increased current carrying ability.
Bottom line if you wish to be as safe as possible & comply with code, don't use any power bars or extension cords to run your tank equipment. Your tank is anything but temporary since most of the electrics on it run 24/7/365 & once it's planted on it's stand, not moving too often. Of course this is impractical for most of us, so we mitigate the potential hazard with proper mounting, GFCI devices, drip loops etc. I guess the best advice if you're in the planning stages for a new tank or fish room, run an extra circuit or two & wire up as many wall outlets as you need & then some..... and use outdoor type covers & boxes that are somewhat moisture proof.