One thing that can help all of us is to learn a little more about your game.  How do you like to generally play the lanes?  Also, can you provide approximate speed, rev rate, and PAP if possible?  That can help us narrow down some of the choices to help you fill any gaps.

I checked out what you have, since I wasn't super familiar with Lord Field.  Overall, this is what I see:

1) Ebonite Pivot (Medium-Heavy Hybrid)
2) Brunswick Lethal Revolver (Medium-Heavy Solid)
3) Columbia 300 Freeze (Medium-Light, Solid)
4) Lord Field Off The Chain (Medium-Light Pearl)

In all honesty, you have a pretty good arsenal at this point.  You have your higher end stuff covered with the Lethal Revolver and Pivot.  The lower end with your Freeze and Off The Chain.  Where I would focus is going to be on your benchmark piece. 

Some examples of balls that can be used here would include the Storm IQ Tour Solid, Brunswick Melee, Roto Grip Disturbed, Columbia 300 Mass Eruption or Disruption.   

The key here is having something fit that is going to be predictable and generally a bit smoother in overall shape.  A good benchmark piece is something that can be thrown and will let you know to ball up, stay where you're at or to ball down.  This is where I would focus since you have the top and bottom halves of your arsenal covered.

If you have a slightly stronger layout on your Freeze, you could have it at 2000 abralon or 500/4000 and it could actually be a good benchmark piece.
If you were to go that route, you should just need something under everything else like urethane or plastic with a core. (Natural's, Taboo Spare, True Blood...etc)

If you have a layout promoting length on the Freeze, then I agree with what's been said about getting something slightly stronger as a benchmark piece with a solid or hybrid cover. Any of Tommyboy's suggestions would work, you could also go with a Crossroad, Arson Hybrid..etc

the Eruption Pro is a possibility...I know it's been getting great reviews and people have been loving throwing it, I'm just not too sure if it might give you overlap. I haven't really seen it in action much, someone else should give you a better answer on that ball

No, the Raptor Attack is a strong ball for med-heavy oil.

thanks . all