While strength and agility will no doubt make a furnace operator quicker, if you have reasonably set up stockpiles near the furnace the operator really shouldn't have to do much hauling, so the effect should be minor. Ditto for most any other workshop type job. If your shop workers are carrying stuff very far, you're setting things up wrong. If your gemcutter only needs to move 2 tiles from the center of his workshop to a stockpile that surrounds it to grab a rough gem, then 2 tiles back to the shop, being agile or strong won't make much of a difference. On the other hand, jobs that aren't just performed in a shop, such as miner, woodcutter, hunter, fisher, and hauler will benefit much more from agility and possibly strength. These guys have to cover a lot of ground getting from one work site to another.
One other issue which I haven't seen discussed in role ratings is the difference in effect of attributes and preferences. Good attributes will make the dwarf better at doing the job every time he does it. Preferences will make the dwarf better at making/using that particular item/material, and will make him happier, but won't make him better overall. If the dwarf likes an item he'll be making a lot of (beds for a carpenter, for example), it's pretty valuable. But if it's something you don't make very often, or at all (bucklers for an amorsmith), then it's not really worth all that much. A furnace operator who likes raw aluminum isn't as good as a furnace operator who likes tetrahedrite (assuming you have plenty of tetrahedrite and use it). So I think attributes should probably have more weight than preferences, and not all preferences are of equal value.
Some of this is dependant on the player as well. I equip my soldiers with a mail shirt and no breastplate most of the time, so a dwarf that likes breastplates won't make a better armorsmith for me. But if you use breastplates, then it's valuable for you. If I have a fort with no layers of gabbro, then I don't care if my mason like gabbro. But if I've got dozens of layers of it, then it's much more of an advantage. This probably means that I should make a copies of the default roles and grid views and make customized versions for the way I play, and for the fort I'm playing in.
Keith