Well... 2 xeno equiped eagles can take down a lib GB with b/b to spare. You just have to be very very careful and dodge like crazy.
1 well piloted bomber can take down a GB.
2 good bomber pilots can take down anything up to a cruiser, and can have a damn good crack at a battleship and take them out if they do a good job... Anything is possible with luck and provided you have good pilots.
But yeh...
2 bomber can take down a battleship, cruiser, battlecruiser...