Synapse sliver isn't bad but the mana is alot for that...
I never said synapse was good, i said it wasn't bad, and it costs alot. It was just for drawing which ninja is alot better and so is curiosity.
Overall there is no really good sliver besides the ones from tempest
Crystalline Sliver
Muscle Sliver
Talon Sliver (worst of these four)
Winged Sliver
Heart Sliver
Hunter Sliver (depending on meta, can be really good)
The rest of the slivers (unless you use overlord and Queen in a fully sliver deck) are just not good, they cost too much and don't do enough. These are the only really useful slivers.
the place you play seems alot like the store i used to play at. If there are alot of creature decks and not alot of Tier 1 vintage decks then you should maybe think about Jitte and Sword of Fire and Ice. These guys can be sick with card drawing and creature control. Standstill will not be the best if there are alot of factories running around, Jitte can take care of them and help you win esp with flying slivers overhead.
As far as running red in the deck do you just not own the red duals? or don't want to? you could run the R/G or R/U instead of mines.