I run a 12" rear cork, and mini guides on all my rods. While the mini guides don't cut down a whole lot In weight. they do make the rods less tip heavy giving the illusion of a lighter weight rod.

I've ran them as small as 2.5mm on the tip section. Starting at with 8mm for the first guide closest the reel, working down to 2.5's for the top 5 or 6 guides.
After a few years of running mini guides for steelhead/salmon rods. I will say that a 4mm is about perfect (so bobber stops can still be reeled up into the guides for storage) I never cast with my stops inside the guides so its a non issue of them catching.

Running those tiny guys really changes the feel of a rods actions as well. Makes for a really responsive rod. I have 2 blanks tied identical, one with 4mm guides and one with 6mm Fuji's and there is a very big difference.