I tried on the Maggie Sottero Reese, and I am usually a size 6. She put me in a size 10 and it was snug.... so I wouldn't get too disappointed. I was in total 'sticker shock' about the sizes of wedding dresses too!
Isn't it funny-- even though it's just a number, it can still bother you!!
And personally--- I would probably just drive the 5 hours to get an idea on fit, then order it from the shop near you-- just to be safe and lessen potential alterations. That's just me though- I had to drive 2 hours to purchase, fit, alter my dress! Bring a friend with you, make a mini road trip of it! Then you won't be so stressed w/ anticipation...