Its not from the above site, but from one of Frank Amato's (Portland, OR) publication, "Flyfishing & Tying Journal", Winter 2005. Unfortunately, the article, "The Spey Fisher's Guide to Sink Tips" is not availalble, on-line, and I try and respect copywrite (some of us do, Voodoofly). But, in summary, here are the details:
Clackamas River, OR, pool selected was one frequently fished by the guide (Robert T. Russell) for steelhead, classic steelhead riffle where they had caught fish in the past.
They sledge hammered a piece of rebar into the stream, mounted a marked white PVC pipe over it, then took pictures and measured where certain activities and combinations placed the fly. They measured how far down in the water column the fly ended up.
Set-up: 14', 9/10 wt spey rod, WC 9/10/11 and 8/9 wt set up. They made numerous trials, and noted different ranges of depth for the same rig.
and Airflo sink tips
Sink Tip Grains Range of Depth(")
Airflo Type 10 (10') 235 22-29
Airflo Type 8 (10') 165 21-27
Cortland LC-13 (10') 130 26-30
Type 6 11wt (15') 166 22-27
Type 3 11wt (15') 166 20-25
Intermed.11wt (15') 166 15-19
Type 6 8wt (15') 109 25-32
Type 3 8wt (15') 109 20-27
Intermed, 8wt (15') 109 14-20
All mends, both upstream mends,downstream mends, and casting 60 degrees upstream were tried, all made a difference in the beginning of the swing, but ended up higher in the water column at the end.