So I've been running OSC a lot. I'll start off by saying, a Maxed out formation is super mean in Apoc. The heavy fire power is often from long range, and so you get your cover save against that. Then you can make the really powerful shots snap fire, and many of the S10 or D weapons are blast and cant fire. You just have to watch out for the larger ones that can target the ground and not you directly.
In normal games, I've found that two Ghostkeels is the sweet spot. The firepower of two of them combined can really tear apart units, or split fire to tackle two smaller targets (rhinos, speeders etc). I run the two stealth squads bare-bones, they are just too expensive per model. I do sometimes upgrade one each for the fusion if I feel I want a little more anti-tank (or if I know I'm going to face a knight, I need multiple angles of attack). I have made one of the squads a full sized squad, when I run shadowsun as my warlord to give a full squad to move with. In that case I upgrade the sarge, give him vector hit and run, beacon and two drones as extra wounds. Then two fusions with targetlocks each.
I always run my ghostkeels with ion rakers and TL fusion. The fusions give me anti-heavy tank fire, and also helps deal with marines, terminators, and monstrous creatures. The Ion has the rate of fire with a high enough strength to still put wound through even with out the best AP, and will mulch through hull points. Plus the longer range is ideal for skirting the distance which is very important to keeping alive. Two ghost keels at 24" killed a knight in two turns, as he had to keep the shield facing the fusion I had on his side.
OSC really wants to push to mid/side field. You want to be in range to do damage, but stay far enough away that your thrust move will keep you more than 12" away including the survivors move towards you. They are great for malestrom missions. The stealth teams are good for hiding further back, grabbing objectives or picking off stragglers that the ghost keels didn't kill all the way. The OSC's main weakness, much like the rest of tau, is close range combat. Units that can put out a lot of fire power within 12", such as drop pod grav, or fast moving assault units, such as Necron Wraiths. This is where the rest of your army comes in.
My favorite combo so far is running OSC with Forgeworlds Y'var jumptide. Ghostkeels want to keep just outside of 12", while y'var wants to be just within 12". They have incredible firepower at short range, and it compliments the Ghostkeels load out very well. I have been using them as zone control. They hover just ahead and to the side of the OSC as it moves across the table. They protect the flanks, kill the heavily armored units the OSC would struggle with and keep units further away unless they have dealt with them first. It has worked so well I think it will be the new core of any army I run. The main limiting factor is being forgeworld, I am stuck running a CAD + formation until their new book is released.