The GTF Limo is simply too long to be effective--you have enemies from all sides taking shots at your excessive size. It's really horrible--no matter the direction, even if you change speeds, quite a few shots are bound to hit you while you are turning. The simple fact is the Limo is too long and not tough enough to be effective. There are quite a few larger ships that work better--the Ursa tops the list as largest but I find it is also one of the most-survivable, due to the top-mounted turret. In a Limo, I can't bring firepower to bear on a target--in a Ursa, I have a turret blasting you to shreds while I keep you above me.
It's not that big at all - heck, the Pegasus is longer from the side. It's eight gunmounts are glory, but you're right, the Potato is better since it packs more of an overall punch. Sacrificing 2 gunmounts, a bit of speed and maneuverability for heavier shielding as well as a secondary capacity more than that of the Artemis is definitely worth it, no? Also, the Ursa's turret doesn't do ****ing **** to your attacker.
For anti-bomber missions, I tend to load up with Tempests and Tornadoes. Tornadoes will usually take out one bomber and severely damage another by the time I get in Tempest range.
Tornadoes don't fire that far, though. Longer than a Harpoon, yes, but I find you can only weaken about two or three of their bombers before you have to switch to Tempests. I usually use Tornadoes against fighters that are annoying me.