The Creator and IGG are right, this is one area where the science isn't exact, and it probably will never be.
SHU rating is inexact versus taste because the capsaicinoids are a FAMILY of chemicals, not just one chemical. Some act fast, but don't linger, others produce more of a slow burn. At this point you are starting to compare apples to oranges, metaphorically speaking.
Even if you had an exact method of getting a SHU for an example, that's all you would have, the SHU for a sample. The SHU for peppers will vary from fruit to fruit, even from the same plant. Batch to batch there will be minor differences in the sauce.
TheHeat and Klyth seem like they are new to the game, and I remember when I was new to the game I had certain fascination with the SHU. But as I started trying new things, I quickly realized it was the flavor I savored.
Try enough stuff and eventually you'll know where to draw the line...sort of. The more you eat, the more your body builds up tolerance. When I had Dave's Insanity for the first time in 2000, I scarfed down half a loaf of bread trying to remove the heat, now it doesn't phase me. If I would have tried Defcon 0 which is WAY beyond insanity (Defcon 0 is the hottest stuff I had IMO, hotter than the Jolokia powder CaJohn had) 3 years ago, I don't think I would have survived the experience. Now I can, but that might just be because I've been assimilated by years of ingesting Defcon.
You'll eventally tire of the "numbers game", because you'll eventually come across some cheap extract that tastes like chemical waste (acetone, acetonitrile), and you'll appreciate the flavor more.