I was just in 8558 and our only complaint was the overhang in the back of the ship. We could not look straight down into the ocean. Cabin 7670 does have a bigger balcony but you will not look directly down to the water either. It is on the overhang. Cabin 8505 looks like it has a 1/2 balcony.
When are you going?
Teresa and Larry
#36-Carnival Splendor 9/16/12
7 night Mexican Riviera
#37-Allure of the Seas 11/11/12
7 night Eastern Caribbean
I haven't had any of these cabins but have several trips on the "Radiance" so I would say 7670 is a no-brainer. It is tucked up against the wall of the aft suite and is a nice nook. Have spoken to folks who had them and it was all positive.
What the heck kind of travel agent are you booking with? They should know these things. If you are one of these cheap people that look for the best deal online, than you are going to get exactly that kind of service. Find a certified Royal travel agent, not an agency. If you find a good agent stick with them, they can tell you about those really good deals that you're so busy searching for online all night.
My travel agent knows everything and anything. All I have to do is call and the job is done. No hastle, no waiting, plus I can hold him accountable for any screw ups. Only time I booked through the cruise line I had to speak to like 20 people to get a ticket changed. If you have the time to go through that, than by all means.