Are Sapphiretech good video cards?

Answer 1

Yes depending on the chipset.
I would go with a nvidia if over an ati because the drivers can be difficult to obtain for ati.
Good chipsets are the 6600gt or higher, or the 7300gt or higher.

Answer 2

Yes they are.

I have a Sapphire X1900GT, and I've overclocked the core clock from 575Mhz to 720Mhz and the memory from 600Mhz to 840Mhz. This required a significant increase in core & memory voltages.

And the card is still running perfectly.

So I would say yeah they are great cards.