VK 45.02B research: t9 gun or turret or turret+t10 gun?

title says asks it all:

the VK 45.02B, all else (tracks, engines, first 10.5 gun) are researched/equipped.

In what order should I research the three remaining parts:

My current plan:

- 2nd turret (20.4k xp) 

- tier10 gun, 12.8cm 44 L/55 (63k)  

and then only do the

- tier9 gun, 10.5cm L/68 (46k xp)

to elite the thing.

(turret needed for the 12.8cm gun) I was just going to ignore that second 10.5cm gun, and grind for the 12.8cm through the turret (83.4k xp) while using the first 10.5cm gun.

Thoughts? Thanks in advance!