I would bet that the lower processing speed is just due to being careful. Congrats on the great results! The DYS application doesn't take very long at all in my opinion, especially if you don't have to do a portfolio.
Regarding the keyboarding, I would let him go ahead and get into it now. I would still do regular writing practice so he develops those physical skills, and oral lessons too if you like, but I think asynchronous development and keyboarding might be a match made in heaven, perhaps more so for a perfectionist. By the time your son's ready for high school or college classes, he will probably be typing at a pretty fast clip.
