Let's go over the Pro's or reasons for playing Sultai first. The big reason is for the four extra infect creatures. If you asked me about UG Infect, I personally would say it isn't good. There is just too much removal and discard in the format. A single discard spell can leave you with nothing but pump spells in hand. In testing, I lost again and again to Jund. The addition of Plague Stinger brings it up to about 50/50. It depends on the Jund build. Jund decks with less Fatal Push and discard increases your odds. The same can be said for more expensive removal in the form of Abrupt Decay. This is the reason Grixis Death Shadow is actually a worse matchup than Jund. They run four Fatal Push and Snapcaster Mage with ways to filter through their deck to find them. Grixis Death's Shadow is more like 40/60. The worst match up (outside notable exemptions) is Jeskai Control. Path to Exile, Snapcaster Mage, Lightning Bolt and Lightning Helix along with counter magic makes it very difficult. It is possible to squeak out a win, but it is difficult. The match up is like 30/60. All of this said is before sideboard.
The cons or reasons against the deck is the fragile mana. Blood Moon can be a pain. This can be managed and it depends on the Blood Moon deck. With smart play and being always cognizant of a potential Blood Moon, it can be managed. Sideboarding can get a player out of these situations. I guess it comes down to what you are comfortable losing to. At the moment of this writing, Blood Moon is around, but not like it used to be. I feel like the omnipresence of Tron is more of a problem than a Blood Moon.
Now for the cards. I'm guessing the most eye catching inclusion is Unstable Mutation. It is better in practice than it looks. For example, you are playing against RG Valakut. The opponent turn ones Search for Tomorrow and Sakura-Tribe Elder on turn two to chump block your turn one Glistener Elf and follow it up with a turn three Anger of the Gods. To their surprise, you slap on Unstable Mutation. Sure they chump, but they can't bolt or Anger of the Gods your Glistener Elf away. It doesn't get a -1/-1 counter till your upkeep. Until then, it is a 4/4. Once you untap, you can protect your 3/3 with Vines of the Vastwood, Blossoming Defense, or a simple pump spell. Unstable Mutation is basically good against any deck relying on 3 damage spells for their removal. I know, I know. It is weird, but it has proven its worth. Over the course of multiple turns, it actually provides more pump. The addition of +3, +2, +1 is six power worth of pump. Not bad for one mana.
The other oddball is Predator's Strike. The idea is basically to remove anything that doesn't pump. I haven't ever loved Apostle's Blessing. I get it. However, it doesn't give me any extra damage. Most of my creatures have invasion already. As long as Glistener Elf does a single poison counter, I am happy. Rancor has been hit or miss. It seems awfully terrible in the face of 1/1 spirit tokens. Keep in mind that Rancor can be seen coming, Predator's Strike is an instant. It actually makes a difference. Having an opponent believe they are chumping a Glistener Elf to only get their creature trampled over with a Predator's Strike is significant.
On less controversial note, I would promote running at least one Sylvan Scrying in a list. When I am out of creatures, it finds an Inkmoth Nexus. When I need a pump, it finds me Pendelhaven. I would never run more, but it is versatile enough to warrant at least one.
As for the mana, it is close. Watery Grave is the most likely to be changed. There are times, not often, that Watery Grave is the land you want to fetch. I'd vouch for the inclusion of the Island and Swamp more than the Watery Grave for things like Path to Exile, Ghost Quarter and friends. Otherwise, I think the mana is close to being right.
A note about the sideboard, there is none as of now. I'm still tweaking. However, with the BUG version of Infect, Shapers' Sanctuary gets better since we are running more creatures. In UG versions, Shapers' Sanctuary just draws into more pump spells or lands too often. There simply isn't enough creatures to support a card like Shapers' Sanctuary.
Final thoughts: I would not run U/G Infect in its current versions at a tournament. It just isn't good for this meta game and probably moving forward. Sure, you will see the occasional list make the top tables. Remember, sometimes you can just run hot. Jeskai is a terrible match up, but it is still possible to squeak out a win occasionally against them. People can also run cold against you. It is a powerful enough deck that it can pull out wins. Looking at the larger picture of the metagame as a whole, it performs terribly. The deck simply needs to run more creatures. Maybe Spellskite can help, but I'm not optimistic. It can work, sometimes. I'd be okay with the BUG version. I'm not delusional in thinking that it will make me a favorite, but it is better.
Just my thoughts from testing and matches.