Hardest Vintage RPG?

Wizardry IV.

Makes even old school MegaTen games look piss easy.

For one's that I've played that come to mind, I guess Zelda II. I didn't play a whole lot, but a friend had it and it was not easy.

One of the hardest games in general?

XCom:UFO Defense. I never owned it (again) and I'd actually forgotten about it until the new ones came out. Still, ff******ckk meeeee, I remembered playing it on a computer somewhere (the same friend that had Fallout 2, maybe?) and it was brutal. Dying and losing are just expected. That's just how it is. Playing for hours and hours does not automatically guarantee you'll wind up in a position where you're going to win the game, and you don't know it until you've invested all that time.

I've never played the original Shin Megami, but 7th Saga is one of the hardest games I've ever played. That's compared to being able to beat Contra and Ninja Gaiden without dying. HARD.

7th Saga is really, really hard.