According to said calculator, the 600 model would leave you $2000 short after 6 months at a purchase price of $4680. Also, the cheaper 300 model would leave you about $1450 short after 6 months after a purchase price of $2800. And those figures are assuming you start using the product in mid-February. If Butterfly labs are late on shipping the cards, and you start in March... forget about it.
I'm fairly new to the Bitcoin game, so can someone tell me if I'm wrong about this? Is it actually wise to purchase either of these cards?
Edit - The short answer is NO, especially for SHA-256 currencies. I spent about $1000 on a 50 GH/s miner. It generated about $30 per week in gross profit, but the net profit was less due to pool fees. Also, my electric bill rose by $100 per month. Luckily, I was able to find someone to buy the miner from me on ebay for CLOSE to what I paid for it.