B-17G

Successor of B-17D, covering the biggest flaw of D model - lacking defensive armament.
Tail gunner covering annoying dead zone in horizontal plane, turrets with wide fire arcs and greater firepower do the job against overoptimistic attacking planes, especially light fighters and lower tier targets. Also shreds enemy bombers, so specializing this version should be much easier than tier V.
Bomb drop the same, unfortunately 2nd load has to be developed for 15k exp.
Plane itself is similar to previous version, so nothing new about the tactics - fly high, pick packed GTs, carpet them.

There is only one issue - tier VII heavy fighters don't give shit about B-17G defensive armament - they just come, fire and go.
Comparing fire effects against attacking tier VI and tier VII heavy fighters, I suspect hidden modifiers to rear gunner efficiency when firing planes of different tiers - lower tier planes are being shred to pieces, same tier can survive, higher tier don't care.