Death Star Line

Starting from tier V they are all slow, heavy assault tanks with rapid fire guns and quite a lot of armour and high DPM. However they each have a gigantic, tumorous commander hatch weak spot. Except for the AT2, which has the hatch in the middle of the tank right above the gun, it is more than possible for you to hide your hatch in certain locations; essentially making you an effective roadblock that can permatrack anything that is foolish enough to rush you. Both the AT8 and AT7 can hide their hatches around corners, making them very difficult to handle. the AT15 has the smallest hatch, and excellent gun depression which means going hull down and using the gun depression to its maximum completely hides the tumour(note however that there is a hole in the gun mantlet; staying at range should help prevent rounds hitting the hole flush and going in).
When you get to the Tortoise you will have a lot of armour. However the armour has quite a few number of weakpoints, and most players at tier IX will probably be packing gold and will definitely try to snipe your cupola. You do get 2k hitpoints and an amazing gun to compensate; try to preserve the Tortoise's HP pool for later in the match, then out DPM everything. This is essentially what you have to do with the tanks in this line.

There are quite a few equipment choices you can use, considering you may not even need EGLD thanks to the excellent gun handling the AT tanks have.
Rammer should be mandatory on all of them, as it further boosts the already amazing DPM. Until you train your crew with repairs I'd recommend having tool box on as well; getting flanked is certain death, and being tracked in the open will get you killed by arty. When you do get repairs, swap the tool box out for vents. For the last slot you could run whatever you want(please don't use camo net for fuck sake). Since these tanks are an arty magnet, spall liner could be of some use. You should also consider optics or binocs, though despite the large cuploas these tanks tend not to have good view range, so it may not be worth it.

Since you are going for the tier X you will want to train you crew with mentor first, then swap it for Sixth Sense, train mentor again, then swap for BIA. train mentor for the third and final time then start working on repairs(swapping that and then training it a second time for track mechanic is optional). After that Clutch breaking would probably be a good choice.