Shieldless tank stealth(?) Cobra:
http://www.edshipyard.com/#/L=602,4yG4yH7sh7sh0Wg0Wg,316Q6Q6Q5K4s5K6k,15O15O15O12G12G12G
570 armour, play around with silent running...
(Am going to try this out just for kicks actually...)
Well, tried this out the other day, though only had class 3 hull reinforcements since that's all the starport had in stock, then did a bit of sparring with a friend in his Viper.
With some careful heat management and silent running, no target lock on me until at least under 1km distance, though visual tracking still works of course. And outside the range where the radar/sensors are able to track properly, I appear as a blinking uncertain contact on the radar, not as a hollow square indicating another player.
Toughness... hard to really say. By the time I got his Viper's shields (only one shield booster, C-rated if I remember correctly) down, he'd managed to chip away about 7% of my hull, but that included having some trouble hitting me as well. Comes with the downside of course that hull does not regenerate, unlike shields, so your time on the battlefield is ultimately limited. But could make for some interesting playstyles...