Reading FTR I see they've changed the requirements now:
the developers apparently decided to make the Object 260 individual missions easier. Here’s how they changed the most difficult missions for Object 260:

- LT: deal 8000 spotting damage (secondary: get 5 spotting kills): primary reduced to 5000
- HT: accumulate 20000 damage – either dealt yourself, or blocked by your armor, they add up (secondary: survive and win): reduced to 14000
- MT: destroy 3+ enemy TD’s, that are at least one tier higher than you (secondary: survive, win and deal 3k+ damage): changed to “of at least your tier”
- TD: deal 10000+ damage (secondary: destroy 5+ enemy tanks): reduced to 8000
How I was thinking for the HT and TD missions you could run a one off query to find which tanks have ever reached that level of damage (or Dam+Blocked) and in what % of their total games.

Partly curiosity and partly to see if there is a chance in hell of the HT mission with the US heavies!