I don't like making it more fuelwise expensive but avaible from T3.
It will change nothing. It still will be the worse medium in game by a far.
It's like making Penals 220MP and avaible from T0. Earlier, cheaper but still not useful.
I think you'd find if you actually used things you'd find out what they're good at for them. Penals are better than cons in almost every way as a fighting unit, dealing nearly double the damage up close, beating out both volks and grenadiers. At 220MP and T0 they would excel greatly.
Likewise, a T-34/76 coming out a minute or two after an AEC or a stuart would be a pretty big deal. It is better than both of those units in nearly every way.
I like the 210/100fu idea, it would both support less used doctrines late game and blend well into 1 heavy tank limitation of used doctrines that leaves lots of fuel to spend. It copies the unique feature of t-70, but in same faction and different tier so its ok IMO.
You're trading half a minute of manpower for almost minute of fuel... cost correlates to time. Unless you're massively bleeding manpower due to bad engagements, you're not saving any time but instead decreasing the speed at which you can produce t-34's.
In the hyper late game where manpower income is reduced but you're floating fuel because you haven't built anything other than an IS-2, sure that makes some sense. But that's really not the scenario we should be pricing the t-34/76 for.