technomafia, Optimum Compound and Polish are kinda outdated products. They aren't *bad* products, but honestly there are alot of better choices out there.
If you truly need a serious compound, consider gettin some Meguairs M95. It's a very heavy hitter that finishes down nicely for a compound.
For a medium duty polish, consider Menzerna Super Intensive Polish. Don't let the name fool you, it's actually a very safe and quite mild medium duty polish (it's not as aggressive as a true compound).
For a finishing polish, you might want to look into Menzerna PO106FF Nano Polish. IMO, it'll give you a better finish than the Optimum Polish will.
Keep in mind when you use these polishes that you might need to do multiple applications to get the desired results. PC's just don't have the muscle that a rotary buffer does, so expect it to take alot of time and alot of applications.
Also, always use 4" pads with the PC for best results.