I'll be following this thread, as I am looking at getting the exact same machine as yours. I'm hoping this year, but I won't be home until July and the wife may have other plans for our limited funds.
As far as the turbo increasing your top speed, not gonna happen. The speed limiting factor on the RTV isn't the motor, but the hydrostatic transmission. You'll get to your 29 mph. top end quicker with a turbo, but that will still be pretty much your limit. Don't get me wrong. The hydro trans is one of the main reasons I want a Kubota over the other brands out there. I don't need a speed demon, but I do need a reliable workhorse, and that's what the RTV delivers.