^yeah i used to have to run like an 80mm stem on my specialized. i'm still only at a 90mm with my correct frame, but at least it's in the realm of a normal stem length. other than that though I loved my tarmac until the bottom bracket decided to quit life.

i think it's kind of funny how with all the high tech stuff on that venge they're still running bb adapter cups.

yeah but specialized uses a non-standard stem/topcap setup iirc (you can adjust the angle of the stem, correct). this bike is pretty standard all around, although i'm not sure what the instructions said...if there even were instructions with the frame.

whatever, i'm pretty confident that the current set with the spacer on top (instead of on bottom) should be good. could probably use a 5mm spacer instead of the 10, but I'm pretty sure it doesn't matter. I agree that the compressor plug was probably slipping, but only because the stem wasn't clamped enough on the steerer, so it should theoretically be good now. if your setup is right (on a standard stem setup) you can ride without a topcap and be fine.
@Enthalpic 5mm above and below with a -17 stem may be closer to my old fit, but it would be lower and I'm not comfortable going any low. the current setup is actually closer to how I was fit sometime last year.