Is there a way to make 6D raw files load faster in LR4?

Convert the raw files to DNG. It takes more time during the import because the CPU has to do a lot of work, but DNG's work faster in LR4 because they take advantage of multi threading.

" Tiled" DNG files divided into parts so multicore processors can read and write them faster."

"Fast-load data," a miniature raw preview image embedded in the file that makes it faster to switch among images in Lightroom's develop module--eight times as fast, according to Tom Hogarty, principal product manager for Lightroom."

Search for an article in cnet called "Adobe offering new reasons to get DNG religion"

I switched to DNG with Lightroom 4 and have been very happy with the performance.