Also to add:

That being said, comparing the OMAP 3430 and the QSD 8250, the first difference in their architecture is that the 3430 off loads some CPU intensive tasks (video, audio, digital signal processing) to dedicated co-processors (GPU, DPS, etc) while the Snapdragon processes all of it in their CPU.

So, if you are watching a video in the 3430, the main 600 Mhz CPU is doing nothing, letting the GPU work on it; while the 8250 main 1 Ghz CPU is busy decoding the video, which probably takes a fair chunk of that 1 Ghz.

It is a different approach to the solve the same basic problem. I prefer the N900's methods as it means graphics can be superior since those co-processors were designed for that architecture unlike the CPU which is more of a "generic workhorse".
And it also means the N900's CPU is free to do more tasks (ie multitasking) and doing so more efficiently than the QSD's; an added benefit.

edit: Read: Anandtech for more details