I'm only testing with the Tier 3 Blenheim IV (Early) at present. It seems you can (should) fly above flak, which for Tier 3 reaches to 2565m and should you be in a Tier IV match, 2925m. It takes a while but you can get to 3000m and stay there. I'm trying:
1) Bomb Sight I (a no-brainer)
2) Engine Tuning I to get me up quicker and away faster too if pursued.
3) Improved Flaps I (to loiter over targets longer?) and for lower stall speed and better turning which seems to be useful up there.
Note that these are all freely dismountable, unlike other options which cost.
Comments on other ideas:
1) I don't see any benefit to protection given you only have 3 slots, as long as you stay up at 3000m. The guns are terrible, front and rear, so Rear Gun Stabilization I seems like putting lipstick on a pig. If someone makes it up there to let me know I'm causing problems on the ground, I'd hope to try to evade with boost. If they catch me (Bf 110 C-6?) it's really time to bale out.
2) Concealing Livery I is moot since you're above flak- just, the jury is still out but a shell exploding at 2925m seems to throw some shrapnel to some (100m?) radius (prioritize High AA Positions on 1st pass?).
3) Self-Sealing Fuel Tank I seems unnecessary, the aircraft seems robust enough and nothing screams fire anywhere.
Skills- Demolition Expert for Pilot, Vigilance for Gunner as lookout, the .303 Lewis is just for show.
My options are pretty opposite to yours on the Tier 3 Blenheim IV (Early), but I've focused on what'll get me up there faster to do more damage quicker, as opposed to protection from threats I've so far found few and far between. Thanks for your post and I'd be interested in thoughts of others too.
Edited by Catch21, 05 December 2017 - 12:26 AM.