Touring - touring ergonomics

what is proper position on a 700c, drop bar, touring bike (520, for instance)? I am familiar with mountain biking positioning, but am pretty novice when it comes to fitting road style bikes.
A guy at a local bike shop said a more horizontal back reduces back pain/strain, is this so? It would seem to me that more direct weight, less stretched out, more upright would be better, but, again, I dont really know.
Thanks
p.s. this is for long, loaded touring

I would agree with your bike shop a straight back with slightly flexed back and abs puts you in a mechanically strong position relative to a stretched out position where much more stress is concentrated on the lower back. This is good posture to maintain off the bike as well in everyday activities as even activities not particularly weight bearing such as cycling or sitting at a desk can lead to problems such as you mentioned over time.
I think for touring in general a 45 degree position is often recommended myself I guess I am probably somewhere close to that though if I am taking in some sights I will be somewhat higher or if riding into a headwind definately lower.

It depends on what you are used to. Experienced racers can tour in a more extended position than other riders.
45 degrees is a good starting point. You can get this with a long/high or a short low position.
Most tourists ride with the bars 1-3" below the saddle.
Touring bars, such as 3TTT Morphe are different to racing bars, in profile and the radius of drops.

what is proper position on a 700c, drop bar, touring bike (520, for instance)?

I think the best answer is "Whatever works for you."

Touring is not really a competitive activity (unlike say, randonneuring), so you don't have to stick to a formula.

My 520 came with a stem that set the handlebars (for me) just a little lower than the height of the saddle. After a few rides I decided to switch to a stem with a higher rise, putting the handlebars even with the height of the saddle. I am not stretched out as much as a racer, but I'm in a position where the load is comfortably distributed between hands and butt. It was very comfortable for rides of 50-100miles.

Just recently I decided that I preferred the setup I have on my MTB/commuter bike. It was nearly identical to the position I had on the 520 in terms of reach and handlbar height, but I found that:

1) I never use the drops on drop bars
2) I prefer the easy access to the shifters and brakes of a flat bar setup.

Now I have MTB-style riser bars, LX shifters and MTB brake levers on my 520. I'm going to flip the stem back down to compensate for the rise in the "riser" bars, and I'll be as stretched out as I was on the drop handlebar, but with a better (for me) braking/shifting setup. And I have MTB barends to provide some alternate hand positions.

So experiment a little. Find that compromise between efficiency and comfort that works for your needs. You probably don't want a flat bar setup, but there are options in terms of height and reach to the drop handlebars on your bike.

thanks for the advice. I expect as soon as I get a bike and put some miles on it I'll figure out my preferences.

In the past I have had back pain or soreness during long rides (a common thing i think among inexperienced riders). is that sort of pain a result of improper positioning or muscles adjusting to new positioning/demands?
Thanks
Q