Yes, the 2" of aperature will make a difference, and is well worth the extra $ if you can afford it. The 6" might make you want to upgrade to the 8" down the road anyways (no guarantees that getting the 8" now won't stop upgraditis from hitting you either )

As far as a scope case, I'd say that unless you plan to do a lot of traveling with the scope, a case probably isn't necessary. I've had the Orion 8" and now have the Orion 10", never bought a case for either of them. I've done a fair amount of traveling with both of them, in winter my observing site is about 40 minutes away, summer its 70 minutes away. I've also taken it to a star party 3 times, 2 hours away, and I took it down to Phoenix just a couple weeks ago - 1600 miles.