Streaming works differently in all 3 cases cited, they're not direct comparisons... this is probably part of why rage faces some driver issues - it's a slightly different technique [plus overheads from the usual bells and whistles available on the pc which can further improve visual quality but require processing time]
But the principle remains - how best to organise data in as best a way as possible and balancing [size] quality vs. [processing] quality vs. vs. [visual] quality vs. load time.
Similarly the benefits in defragging your hard drive simply depend on how fragmented your hard drive actually is. If your constantly filling it up and it was a 6 months since you defragged then chances are everything would benefit from a defrag - especially games that attempt to stream large files.
Depending on the available ram and configuration - from my
limited experience - I've found it perfectly possible to be loading 8192 textures in with a bit of compression, not max alias/anisotropy settings, with reduced use of mipmap/lodding [to keep textures sharp at distance but presumably often loading larger versions], with no noticeable pop in. But your mileage may vary depending upon pc config and cfg settings <- I would recommend tweaking these as much as you can bear

... donotargue.com/cfg-makers/rage/
Not a great answer but perhaps start with low settings to make sure you can load textures without pop in and then up it from there.
The console versions use 4096 page files and after hd install experience limited pop ins on extreme changes angle changes or when under shader stress.