I can't find specs for the exact drives in the 360/PS3, but seek times for generic drives are easy to google. Seek times for a 12x DVD drive seem to be in the 100ms-120ms range, while 2x Blu Ray is around 350ms. (In other words, DVD seek times are 3-3.5 times faster than Blu Ray.)
Also, what is this about Uncharted having no load times and streaming all data? I have nothing against the game, and it'll be the first one I buy if/when I get a PS3. But the part I played at a friend's house had plenty of loading. Sure, the word "Loading..." never popped up on screen. But every time a pointless and unskippable cutscene plays, that's a load time. Drawn-out scenes showing a doorway closing behind you as a door opens in front of you - that's not even a well-hidden load.
