I have owned T3s and 75s in .243 and .222.
There is very little to choose between them, and for the average stalker under field conditions, no measurable difference in accuracy or performance.
The key differences are:
75 can be top loaded (double stack magazine and big ejection port). T3 cannot.
75 has more magazine capacity (in .243 it takes 5, while T3 takes 3).
You can find 75s that have not been screw cut and which have 22" barrels. This is much rarer with T3s, which are almost all 20" barrels. This may be a consideration for 6.5x55, which I understand benefits from a longer barrel.
75 has an extra button by the safety catch that allows it to be unloaded with the safety on.
75 has several different action lenghts, scaled to cartridge family. T3 has one size fits all action.
75 has integral recoil lug. T3 has separate 'floating', aluminium, recoil lug. Much debate about whether this makes any difference.
Fit and finish on 75 on balance probably better - feels sturdier.
Mostly metal parts in 75, some plastic in T3. Only place where this may make a real difference is bolt shroud, which has a reputation fir cracking eventually in the T3.