The angles of 80 or 84, compared to a 73 are only 1-2mm shorter due to the slight rise. It's simple trig. The 80 degree has about a 7 degree angle with the ground. Multiply cosine7 (.99) times the stem length to get the horizontal length.
The other issue that has not been mentioned is stems are now measured differently than they were in the old days when virtually every stem had a 73 degree angle. Back then you could lay a scale along the top and get the correct length, like 110 or 120, but a modern Ritchey stem in a 110mm length and 73 degree angle will meaure about 115mm if you lay a scale along the top. That's because the measurement is really taken along a line parallel to the extension, but through the center of the bars.
Last edited by DaveSSS; 12-16-09 at 03:46 PM.