I have some simple questions:

I will invest the minimum 16 BTC;

What will be the monthly gain ?

For how long?

I have read the spreadsheets; you must consider that I want my BTC back as soon as possible, so I choose the fastest variant of investment.

Thank you adraza for your interest.

16btc @$13.00 (which seems to be very close to all of the major exchanges right now) =$208

That would most likely allow me to purchase at best a new in box with warranty 5830 within the next few days.

A 5830 is listed by many seemingly reliable sources as capable of 244Mhs.

My test system (fairly modern Win 7 system) has an old Nvidia 8800 GTS that puts out a paltry 17.9mhs. which has generated just under .01btc/day using deepbit and a touch less when using slush's pool.

So assuming the 5830 puts out 244mhs, and the difficulty remains about the same, the system should generate about 0.12btc/day or about 3.74btc/month.

Whatever is left over for the price and shipping of the card will be returned ASAP as your first re-payment.

You are chosing the fastest repayment option of 70%, therefore I will make monthly payments of 1.83btc if difficulty remains the same until the principal is paid in full. 16/1.83= 8.74 therefore your principal should be paid off within about 9 months.

Once the principal is paid in full (change left over from card plus monthly payments) the following three months will be paid off at approximatley 0.79btc, 0.52btc and finally 0.26btc. I say approximatley because barring disaster I plan to pay you back the full total of 17.6btc (principal of 16btc + 1.6btc interest) so that you will have a minimum profit of 10% on your investment.

Please let me know if the above answers your questions to your satisfaction.

I humbly thank you again for your interest.