The wattage doesn't refer to how much the bulb is actually pulling. LEDs by nature require MUCH less current than filament bulbs to do the same work, unless you're working with high powered LEDs. (the kind that need large heat sinks) That is an advertising mechanism for you to equate a brightness reference to. Think about it, HIDs are offered in 35W and 55W options, LED headlights setups that are of comparable brightness come with drivers and large heat sinks on the back. A pnp bulb isn't going to be nearly as bright or use the same amount of power.
Also, you don't want to be married to the idea of the brightest bulb possible. These bulbs are for line of sight for driver's behind you, not lighting up the road. I don't think it's ever happened, but say you've got some insanely bright brake bulbs and you catch a cop behind you one evening who had a bad day. Maybe he gives you a ticket because his retinas have been fried and he still sees spots after you let off the brake pedal.
An extreme scenario, but you want to take other drivers into consideration.
I'd never make a sweeping generalization. LED bulb technology is constantly changing. If it's not advertised as being dual socket compatible, either ask the retailer selling it, or find one that does. Last thing you wanna do is assume you're buying something, and blow fuses when you install them because you weren't 100% sure.
This is purely subjective since it depends on how much night driving, and/or city traffic someone might drive in, but I'm sure some will be able to recommend what they are currently using.
Polarity of the bulb is not the issue. The socket is physically wired different with pin placement. See below.
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