obj. 277 or IS-7?

I haven't played the game in a long time (at least 4 years) and started the grind again a few days ago. I used to have the IS-8 (the tier IX Russian heavy tank) which is now split into the t-10 and the obj. 257. I now have both these tanks and I am now deciding which one to grind out first.

I compared the IS-7 to the obj. 277 and as far is raw numbers go: the obj is superior. Here is my conclusion:

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Firepower:
– obj has 100 more alpha

– obj has 15 more pen

– obj has more rate of fire

– obj has better aim time and accuracy

Survivability:

– is has more hp

– is has 10 more hull armor but still only 150 which seems very low to me, even when angled correctly

– obj has 50 more mm turret armor, which would make it a good hull-down tank

Mobility:

– IS has slightly more acceleration

– IS is 5 kmph faster

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Stealth:

obj is slightly more stealthy

From all these numbers my conclusion is that the obj is a much better tank. Trading off 10 hull armor for 50 turret armor seems like a good trade. However, I know a tank is not just its stats. maybe the obj 277 crew gets killed quickly or something. I would love to hear some opinions on this.