quality of parts used such as resistors capacitors and inductors could make the card slower than it should be. Also, to some important people, Different makers have different heatsinks that provide overclocking ability. Some manufacturers have high overclockability than others.
Sapphire makes most of the built by ATI cards, so they're good quality. Tyan makes server motherboards and uses their own design for their video cards, but they're known to be rock solid too. Read reviews of both and see which one you think is better. You really can't go wrong with either.
3.3ns on 9800np are in fact 2.8ns chips labeled as 3.3ns with different timings in the bios, a flash to 9800pro bios will "get them back" to 2.8ns specs (~)
As for quality, well check out This baby ... that's quality... quality can be seen as "where the hardware can do more, for how long, what are the components (good ocable graphic memory, a good HS, as VIAN said, good bundle even since some ppl look for what goodies come bundeled (games, softs, cables, adapters, readable manuals) all that make these few $ more or less in a buy make sense.