Agreed on all points IRONFIST, just a difference of approach. I'm single and the people I care about are where I'd be traveling to. Push to shove I can go two-up if I want/need to bring someone else. I can carry everything I need (arms, three days worst case of food, ammo, and clothing, a roll of tools and repair supplies for the bike) in hard cases or on my person. Hell, I can fit everything except my MBR and the cased ammo in my big messenger bag and be gone in ten minutes. I think in terms of the old fighter pilot's adage 'speed is life'. I don't need protection from the threat, I need to get away from it, around it, or kill it,
quickly. Avoid contact whenever possible, then run, then fight. If it comes to a protracted firefight, yeah, I'm boned, but from the avoiding/running aspect I can be way more elusive. I don't ever want to be in a position where 'soaking up bullets' is my best option, but I'm funny that way.
The other aspect, gas mileage, is because I wouldn't plain on being stationary. If the initial situation deteriorates further my original safepoint might have to be abandoned. A siphon and an abandoned car and I'm back in business. Once at a safe place, I ditch the luggage and I've got a fast scouting platform. In any case I'd have an ongoing need for gas, which is why fuel efficient makes more sense to me.
Although your multiple bike idea intrigues me. A pack of motorcycles, sweeping down on an unsuspecting village like modern day cavalry... yes, very interesting...
Edit: Not to go off topic, but suddenly I thought 'Wouldn't it be smart to plan for multiple vehicles?' Then you get the best of both worlds. A thumper/ATV to scout ahead and a larger vehicle to act as your base/hauler/battering ram.