Rick,
I used to use the SA shooting heads in type 3 and 4 prior to RIO putting the 15' already looped tips on the market and I cut the 30' head into 2 sinktips, one of 17' (it had the front taper on it) and one of 13' (it was the rear of the shooting head) for my fishing. After about 3 years, I quit carrying them in anything other than 15' because there really wasn't that much difference between the 13' and the 17' and it reduced the number of sink tips I carried.
Since RIO has the 15' in types 3, 6 (like Juro said, it is nearly identical in sink rate to SA type 4), and 8 (far easier to cast the 12'-15' of SA 550 gr Deep Water Express and it sinks about the same rate) I no longer make tips from SA sinking shooting heads. I do, however, carry a 12.5' piece of SA 700 gr DWE when using my 16' 11 wt in winter for when the water is in the willows, but dropping and clearing, and I also carry 13' sections of SA type 2 when summer fishing and want to get down just a tad in low water.
I use the bottom line designation of the spey line to figure the proper weight of the SA shooting head (i.e. I use an 8 wt on an 8/9 spey line). I had been using SA sinking shooting heads for years to make interchangeable sink tips for my single hand rods and just used the same technique for the 2-hander. The only difference is with the single hand line, I found the sink tip works best for casting if I drop a line size from the line's designation.
This approach has been used for years. I first used it back in the early 1970's when living in Pennsylvania because I couldn't afford extra spools for my reel since I was a poor college student. I thought I had hit on something new and was all set to send an article on it to FLY FISHERMAN, but then I saw an older angler using the same thing on the West Branch of the Delaware River. He told me he picked it up on a steelhead trip he make to WA state in 1968. There went my thoughts of making a bit of cash to buy another reel for what was obviously not something new.