That would be waste Harold. If you really want slow speed the variable speed 6" gets plenty slow as is, and you can very easily grind at full speed without fear of burning the edge. In my opinion WAY TO MUCH is made of the risk of drawing temper. Keep your fingers somewhat near the edge and you will feel the heat well before you burn the edge. I had NEVER ground a blade before I got my 6" PC grinder and I was using it at full speed, with the gray wheel and rests (that the magazines say you need to throw away) within a week of getting it without any problems. I will occasionally burn a corner ever so slightly if I'm just flat out being to aggressive but it is not AT ALL hard to avoid. Burning and edge is not something one should fear, it is simply something one should be aware of having the potential to do. I do think a more friable wheel is nice just because its faster, as it both grinds faster and requires less quenching and dressing, but it is not a requirement.
Sorry for the rant. I'm just a big believer in a standard 6" grinder, and I rant sometimes about it because I kept putting off buying one thinking that I had to be prepared to spend $200 or so just to get started ($40-$100 for the grinder, $50-$100 for tool rests, and $40 for a new wheel, plus more if I wanted to balance the wheels). This is not and was not the case, and I'm soooooooooooooo glad I finally just bought one for the $80 or whatever it cost and used it as is...my only regret ever was that I didn't do it sooner. That PC or equivalent will work off the shelf with the gray wheels and stock rests. It comes with a dresser as well as a little water dish, and has everything you need to get started hollow grinding. I'm not saying not to buy after market rests, and I'm not saying not to buy more friable wheels...they are legit improvements, but know that in spite of what the mags say, they are not a requirement.
Happy grinding. Rant over.