I always use the spec sheets for the bridges I buy. I usually double check with the actual bridge I receive to ensure I got the proper unit, but the specs are the reference for the guitar's design and layout. I've used many different bridges and the specs are always dead on accurate.
Wes - If you had read my post, I did mention that it appeared as though the SM Schaller was different. Schaller has different models. It might be best to contact them directly and ask them.
Its always best to get the exact model number and get the specs for that exact model. Measuring can introduce a factor or error and when unsure correlating with the specs are the way to go, but that might be because of my engineering background. The specs is what's used to produce the bridge in the 1st place.
For the stuff that I buy, I've never had issues with erroneous specs. I tend to prefer quality hardware and the specs are dead on for all the bridges I've bought so far (Boogie Rails, Gotoh, Floyd Rose, Ibanez Edge, Fender, Wilkinson).