Remember, numbers are still a work in progress and might change (although considering past tests, they are unlikely)
The experience showed is only when directly skipping every single tank straight into the next tier, without researching unnecessary modules to save XP.
Listed numbers represent the tank to be researched = base XP cost for the research of the new vehicle / how much does the entire grind to go directly to the vehicle costs (e.g 236k XP needed on IS-2-II when researching IS-3-II)
IS-2-II = 51.300 ex. – This experience can be accumulated in advance on KV-3.
IS-3-II = 165.400 ex. (For the tank) /236.300 ex. (with the necessary modules)
ST-II = 217.000 ex. (for the tank) /544.100 ex. (with the necessary modules)
In total: 544.100 exp. We highly recommend (based on preliminary XP values) to save up 51.3k XP on the KV-3 to have IS-2-II researched on day 1, and at least 50k to skip horrendous stock grind on the IS-2-II (Twin 85mm guns at tier 8).