How good would a M1 be without computerized targeting system?

[Mohoender]

We had several discussion over tanks but my question derives from the thread I just posted on aircrafts. We agree that an M1 Abrams is an impressive warbeast. However, maintaining its electronic working under T2K condition would be a real challenge (equally true for most tanks).

Then, How good would be the most modern tanks (M1, T-95, Challenger, Leopard II) with an unreliable taregetting system, or worse without it?