Its a good question,  personally id do the blades since you can have them tomorrow vs. waiting till next year when the difficulty level is said to continue to skyrocket upward.  You'd be better turning over what you can now, rather than wait for later (IMHO)  Use this Link to help you decide a little better:  http://mining.thegenesisblock.com/  

You could also look into these guys: http://drillbitsystem.com/products.html  They seem to have a good rep, and are talking delivery in the next couple months.

As for speeds, just like any frequency out there-  MH/s(megahashes/second>GH/s(Gigahash/second)>TH/s(Terahash/seecond)


1000GH/s= 1TH/s