Hi, got your PM so I'll help you out a bit.
First off, Metagross is my favorite lead in the Gen 4 metagame. It beats the vast majority of common leads in the game. The set you have going is okay but it could be a lot better. For starters Quick Claw is a hax item and is generally not allowed (I believe PO still allows it and I've lost a handful of games because some random nub has a Quick Claw on his Donphan or some sht). Switch it to Lum Berry which cures sleep from lead Sleep Powder or Wil-O-Wisp from Rotom. The EV spread gives Metagross enough bulk to live Fire Blast from Azelf and Meteor Mash + Bullet Punch it to death while the Speed investment lets you outspeed other Metagross leads and Earthquake them. Meteor Mash is super powerful STAB that has the rare chance of getting an attack raise and it's important to have Bullet Punch on lead Metagross because it is a priority move. Here's the set you should use:
Another thing I noticed is that Jolteon and Scarf Rotom will destroy this team. With Jolteon's blistering 130 base speed and Rotom's Choice Scarf they can outspeed and take out Starmie, Gengar, Togekiss, and Gyarados. One of the blobs such as Snorlax or Blissey can help with this. The first thought is since this team looks more offense heavy, Snorlax can replace Slaking mainly because Slaking is practically worthless in 4th Gen OU. Sure it has amazing attack, but being forced to loaf around means that it can never stay in for more than a turn which can allow a lot of pokemon to set up on it. Here's my suggestion for Snorlax:
Third, I'd suggest replacing Togekiss with Calm Mind Jirachi. This gives you another safety net against things like Jolteon and Rotom. Even though you trade a flyer for something weak to Earthquake/Earth Power, Gyarados and Gengar should be enough. Calm Mind Jirachi has better bulk than Togekiss and is a bit more versatile. Here's the set:
Lastly, some nitpicks...
Shell Bell --> Leftovers and Aqua Tail --> Waterfall on Gyarados (just realized how old school Ice Fang/EQ is on Gyarados X_x)
Since you lack a scarfer after replacing Slacking, I'd put a Choice Scarf of Gengar. Substitute + Life Orb isn't too productive without Pain Split and Shadow Ball is a must on Gengar. I'd roll with this:
Well that was just a quick rundown. If another apparent threat arises you can always post back in this thread.