excavate 30 on a mining chunkloader turtle.
Take a lot at the Advanced Ore Quarry program mentioned here. It's Excavate on crack. Turtle digs all the way to bedrock, then starts moving up, mining every 3 levels checking top and bottom, comparing against the first 4 slots of it's inventory to see if they are noise blocks or not. if they are, it doesn't mine it, if they're not, it mines it. Want it to actually dig the big ol' hole in the ground? No problem, give it glass or any other player-made only block as a noise block, and it will dig the hole of the size you specify it to. And deposit everything in the chest, which is very nice. Refueling is also taken care of, in a chest placed on the left of the starting position of the turtle, and it will automatically refuel from that chest when it needs to. It runs 3x faster than the excavate program, on average, because it uses much less moves, and for the same reason, it's much more fuel efficient. 8x8 hole doesn't even take a full stack of charcoal. It doesn't misses ANY ores, and, what's more, give it a chest, and if it sees any chests in the way, it will take the items from the chest, then mine it.
One of the best turtle mining programs floating there. I wanted to give MLG Branch Mining a try, but i never bothered to set up the required infrastructure, though i have to admit the screenshots and videos look REALLY awesome. The OreFinder program is an interesting one, though i didn't compare the efficiency against the OreQuarry, but it functions digging straight down, coming up checking every side for noise blocks, mining everything else, and then moving like a Knight in a Chess game, covers all ores in a given specified area without actually digging everything up. It's extremely efficient in the sense that it mines a minimal amount of cobble and dirt compared to the ores it gets, but don't know about fuel and time efficiency.
The one i'm REALLY interested in, is one that's still in development, and it's the Swarm miner. THAT looks like it will end up being the one that will get mining turtles nerfed. Master Turtle + GPS, controlling however many "module" turtles you give it, that all work in tandem to clear out an specified target area. Since it's using GPS, this can be anywhere up to 384 blocks in radius around the GPS cluster(If it's placed at max height). I don't know if there will be a limit as to how many you will be able to have operating at once, but oh boy, just imagining a swarm of 100 turtles mining out an absolutely INSANE amount of resources is pretty awesome. And what more would you do to craft the turtles, other than creating a program for crafting turtles, that craft turtles for you, and integrates them into the Master Turtle/GPS system? Turtleception.
Have to chunk load the whole area you want to mine, though. Else there might be problems. Program isn't running perfectly yet, issues with turtles mining one another, but i'll use it even if it ends up being less efficient just for the coolness factor of having a turtle army. I like it.