You've stepped up in class of use.

You'll need a GPU that can handle it, some MBP chipsets can... but only just. The bigger and more expensive ones also do nicely. Longevity for AVCHD processing is short lived at this point.

But if you are going into full blown Video Editing and cuts and so on...

Mac Pro here you come. They start at $2499 and goes up to about $20,000. Final Cut Studio is about $1,000.

Good luck.