The accuracy of Slayer Darts is affected by your mage bonus (go kill the metal drags in RuneScape Gold rune , and then compare it with Mystic, you'll notice a huge difference). Damage, however, is not. The same thing happens in mystic, as you would in rune.
As for"black sally," it's really only worth it if have a high defence level or are using blitz/barrage in order to avoid. Sally is slightly more reliable than slayer dart I believe it's hit more frequently at 70 mage than the dart slayer hits at 70 mage. Unless you have 85+ def or an 82+ magic score, it's probably better to choose slayer.
The 78-80-80-80-80-80-80-80-80 long at all, maybe one or two days, and possibly up to a week when you're working slowly. I personally prefer to train on Green Drags, or Blue Drags in Taverly Dungeon if you uncomfortable with the wild. It's a slow process., but it is decent for cash.
If you're looking to get more experience. and speed, I'd look at Yaks, Experiments, Flesh Crawlers (SHoS), or perhaps Rock Crabs. Each of these options will be able to provide decent exp, as well as being pretty casual and with low risk.
For Summoning, it really depends what charms you possess. If you've got the charms, it'll surely take only one day, maybe even less. If you don't, god knows the time it takes you to Buy RS 3 Gold find the charms. I will go under the assumption that you already have the charms.