This option is now missing from the video options and a quick check in the console shows it's disabled by default with the only way to enable it being via console command. (Have tried to force it, vt_useCudaTranscode 1, via launch options in steam and with a rageconfig.cfg file but no go). It only takes if I manually enter it into the console after launch but I don't want to disable my achievements to have this enabled as it should be. (GTX 480 here, R285 beta drivers as suggested.) With it disabled I can see it's utilizing my CPU instead of the GPU as intended.
Edit #2: Nevermind. I thought I had a good workaround but I guess not. Even when forcing it on; after loading a save game it's turned back off again. /sigh