QUOTE(Pheidias @ Nov 20 2006, 07:06 AM)

You would have seen drops on the 360 if it didn't have a extra chip doing the scaling so it could fool people into thinking the games are 720p when they aren't

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This is the correct way to handle it. If the game doesn't run at a smooth framerate then lowering the resolution is acceptable. It is really nice that the x360 has the capability to render at any resolution between 480p and 1080p as needed so there isn't a big loss is resolution when your display doesn't support a particular HD mode.
Unfortunately the PS3 doesn't have the luxury of rendering at hybrid resolutions because of the lack of a scaler chip.
Don't constrew the lack of a feature as somehow being a benefit.
QUOTE
If your seeing drops in 1080p i'd guess its cos the 360 never where meant to do 1080p and the built in chip scaler can't upscale alone so they need to draw some power from either the cpu or the gpu.
It is already known that some games when in 1080i or 1080p mode actually render in full 1080p resolution. There will be a lower frame rate when rendering in 1080p when compared to 720p.