of course, updating a cubemap includes 6*RenderWorld. Depending on the complexity of your scene this may be slow. Copyrect will work with the same speed, no matter how big your scene is. Although Copyrect's not very fast, it's still bearably quick when you use the 256 texture flag (vram residence).
In the code archives there's some code to make cubemapping faster. I think it uses 6 cameras, CameraViewport etc. to render the 6FOV in one Renderworld. (tho this limits the resolution of the cubemap somewhat).
Finally I would suggest to render only one cubemap because there is no need to render mutliple cubemaps! IMHO it's a fatal mistake to assume you'd need to create cubemaps for every cubemapped object! The reason why is: whatever is reflected on an object, it's all relative to the player camera, and not to the object! So unless you have a splitscreen or something, you only need one cubemap, it may be used for all objects, no matter if they are near or far. I already discribed this some time ago:
so the cubemapping camera has to be positioned at the same x and z location as the player camera, but the Y position needs to be as much below the ground as the player camera is above the ground - something like that. But after all it's not an exact science, so be prepared to fiddle for a while.
In the code archives there's some code to make cubemapping faster. I think it uses 6 cameras, CameraViewport etc. to render the 6FOV in one Renderworld. (tho this limits the resolution of the cubemap somewhat).
Finally I would suggest to render only one cubemap because there is no need to render mutliple cubemaps! IMHO it's a fatal mistake to assume you'd need to create cubemaps for every cubemapped object! The reason why is: whatever is reflected on an object, it's all relative to the player camera, and not to the object! So unless you have a splitscreen or something, you only need one cubemap, it may be used for all objects, no matter if they are near or far. I already discribed this some time ago:
_________>o main game camera
______/
_________/___________________ground (not doublesided!)
\.......
\.........>o cubemapping camera
so the cubemapping camera has to be positioned at the same x and z location as the player camera, but the Y position needs to be as much below the ground as the player camera is above the ground - something like that. But after all it's not an exact science, so be prepared to fiddle for a while.