Hmm, now that someone mentioned the super heavy cannon, there _is_ that route...
Suppose you're more of a "how" than a "can" man (m/f). This means two things: Your final gun won't fit on a medium chassis, and you're using a tank destroyer of some kind.
Using both tanks and TDs, you won't be using too many TDs, so you'll get plenty of breakthrough from your tanks. How little your TD provides doesn't matter much, so you can go fixed super-structure if it's convenient. This means med. TDs with heavy cannons is an option, as are heavy/moderns with SH cannon.
As for cannons for the TD, high-velocities require AT tech and heavies require AA or AT. And mediums? They don't have enough piercing unless you mass them. But ...
Since the heavy how. doesn't fit on a medium, you'll want to get moderns or heavies eventually. One is 1945, the other 1943. And if you go the heavy route, you can take a short detour to super-heavy if you want to. This gets you the super-heavy cannon for a single extra tech instead of doing all of the AA/AT branch.
So: We first work towards imp.med. chassis with imp.med. howitzer, with a side-order of med. TDs with basic heavy cannons (good pierce and decent attacks), then work towards adv.hv. chassis with hv. howitzer, with a side-order of hv. TDs with SH cannon.
Yes, we're missing out on some TD boosts from AT tech, but it's still *very* powerfull.
And yes, heavies are expensive, but by the time we're building them, our armies are limited by supply, fuel and manpower, not just ICs, so the difference isn't big. On the other hand, the difference between getting a 1945 tech and two 1943 techs is quite big, so we can begin building earlier. On the third hand, we _are_ missing out on 30% reliability. Fourth, both adv.hv. and modern have 75 basic armour, so we *are* well-armoured, even missing those 30% reliability.