First, You can see the historical different increase here at the bottom.
http://bitcoinwisdom.com/bitcoin/difficultyYou can see the difficulty went up 20-30% in less than 2 weeks.
I would also suggest you to take a look at this page.
http://bitcoinwisdom.com/bitcoin/calculatorYou can change the figures in the profit calculator to see how your revenue is affected by the difficulty adjustment.
By comparing the revenue with the cloud mining hashrate price or the hardware price, you can get some idea about the profitable.
If you are talking about TerraMiner IV with $5999, I guess you are talking about the batch that is "
expected" to be delivered in May 2014.
Please note that, the difficulty change in the coming months will severely affect your revenue when you finally get your hardware, and the delivery could be delayed.
BTW, you should separate your post into several paragraphs, so that we can read it more easily....