I have a 4GB 360 so have had to install the mandatory portion to a USB stick - bought the official 360 SanDisk version - and am running the game off the DVD with zero issues [apart from the noise]. Now I'm used to the 30fps it seems fine, and any dips lower are tolerable. I am certainly seeing
no 'pop' apart from shadows changing as you get closer... so if its happening, then it must be very subtle, or a long way out [see Skyrim for bad 'pop']
I have noticed some terrain tiles look blurry if you position the camera quite low, which looks like poor filtering on the 360 version.
I jumped on a train last night, and just rode it across the map... the detail and variety of the terrain is very well done, will little obvious repeating, or tiling can can plague open world games... and the atmospheric effects are breathtaking... it also brought home how vast the map is.
I think its a visual marvel, regardless of platform, and my only major gripe is the resolution and jaggies.
I wonder how the game would tolerate the play disk being installed to a second USB stick, just to get rid of the drive noise?... I may give it a try.
From what people can make out, they built the game to stream assets from two sources, HDD (mandatory install) and DVD. Installing both discs to the same HDD can prevent some objects/textures loading quickly enough so they can pop-in.
So choices are,
Install both discs and put up with it or not notice it
OR
Only do the mandatory install and play from DVD
OR
Do mandatory install and install the play disc to a USB stick/USB HDD