If you're serious about restocking, you should be looking for items at several MILLION per restock (I don't really bother with shops that don't have that potential). I'm in the process of writing a restocking guide (with individual shop reviews) for my site,
http://www.neofaerie.net.
Some shops to try if you're looking for big profits and you know what you're doing: Magic, Stamps, Royal Potionery, Battle Magic, Defense Magic, Toys, Plushies, Merifoods. There are tons really. =P
EDIT: whoops missed the part where you're on a slow connection. Maybe try clothing (sometimes the shop is fast, sometimes it's okay), spooky food, and less popular shops like Magical Marvels, Snow Food, Icy Crystals, Haunted Weaponry.