You need to work with a budget.
a mac mini can if you are me, set you back $1600 (and I expect to see a new model with 4th generation Core i7)
the iMac 2013, you can spend from $1200-$3000.
The Mac Pro you list won't run anything past 10.7.5 but should be cheap $300. You can upgrade to 8-core for $100. 16GB RAM for $100.
Disk drives would almost be the same no matter what, but you will be looking at external and USB3 or Thunderbolt in some cases.
The 2009 are or were good value, everyone is buying up used and refurbished of that and 2010 now.
Turning one into a 6-core 3.33 is popular, 32-48GB RAM and adding PCIe SATA and extra SSDs.
The 2013 Mac Pro is expensive and then you add monitor, and of course you have to include the cost of external drive cases and controllers. Plan for one and you might want to drop $5 grand on a full setup.
If you editing pays it will pay for itself or should or you aren't a candidate for the newest Mac Pro and the mini or 2009 would be better as Grant points out.
What you don't mention is if yours is a 2010 MacBook Pro? 4GB RAM is low. Head to www.macsales.com and see if yours can take 8GB or more, and look into putting a 500GB SSD inside to beef it up, then look for ExpressCard and add eSATA or USB3 (or both?) for faster disk I/O externally. Go with the "one upgrade a month" installment plan.
IF your system has a half way decent video and processor for doing what you want of course.
There may be some benchmarks on www.Barefeats.com on the programs and your Mac, definitely for FCP-X though.
Apple Refurbished Mac Pro list. They go fast. The 4-core 3.2GHz may be more t han you want to spend.
http://store.apple.com/us/product/FD770LL/A/refurbished-mac-pro-32ghz-quad-core- intel-xeon-2012