The Radeon 6850 is more powerful than the GTX 275.
The Radeon 6850, like most other modern AMD cards, runs its shader frequency equal to its GPU frequency, hence it's combined as GPU frequency and there isn't a separately listed shader frequency.
The difference in the PSU wattage is not something to complain about. Wattage doesn't really matter anyway; +12V power delivery is what matters as far as power delivery goes.
What are the rest of the components changes, if any?