If you are an AMD/ATI user, and are having massive stuttering issues, turn off Catalyst AI in the Catalyst Control Center under Gaming > 3D Application Settings. This was my number one problem, and disabling Catalyst AI fixes it.
I've used some of the same launch commands as Creston, but I found the various 'compression' cvars had no effect, at least not at fixing the streaming or missing textures.
The following greatly improved the texture streaming for me. I still get some, but nowhere near as much as before.
Make this file /rage/base/rageConfig.cfg and add in the below.
vt_pageimagesizeuniquediffuseonly2 8192
vt_pageimagesizeuniquediffuseonly 8192
vt_pageimagesizeunique 8192
vt_pageimagesizevmtr 8192
So now the framerate is excellent, textures look good (mostly), but a lot of holes in the textures and texture streaming is still an issue.