At the moment I am mining with my single Hd 5850 because I happened to own a Hd 5850 before I even knew about bitcoin. I recently bought some new hardware for my computer which I have also wanted before I knew about bitcoin. Obviously the cost of these purchases can't be deducted against any money I make from mining because I would have made them anyway.
Now for the tricky part, I have wanted a 2nd HD 5850 for quite awhile because that would be roughly all the horse power I need for the gaming I do. I have found someone selling 2 of the card I want ... sounds to good to be true right? It is. He is selling them at a price I feel uncomfortable paying. I am thinking well I might as well buy one to go with the one I already have because the amount I paid over the odds with be recouped easily from mining with them. However the other issue is should I got for the second one and then I would have 3 Hd 5850s.
I could then have a dedicated mining rig with 3 Hd 5850s in it, but going for that 3rd one increases the cost drastically because I would be buying it just for mining so I would have to fully recoup it's value for it to be worth it.
Here is a simple summary:option one - I buy one of the HD 5850s
cost to recoup: £10-20 I pay over the odds (I obviously only need to mine 2 bitcoins with it which should be pretty easy).
option two - buy both of those HD 5850s so I have 3 in total
cost to recoup: £150-175 (need a second case, a sempron cpu and obviously the cost of the Hd 5850 i'll probably need some more fans as well which are $$$ :S).Summary
Up until a week ago my single Hd 5850 was pulling in a rather nice 0.2ish bitcoins per day (it wasn't dedicated so not mining all the time, would have been closer to 0.25+ if it was dedicated). Since then it has dropped to 0.125 per day after the difficulty increase. So 3 dedicated on current difficulty will net me 0.375 roughly per day. Obviously if target stays how it is and all variables remain the same etc etc etc I could recoup the cost in just over a month and anything after that is profit plus a heater in the winter
. The trouble is the difficulty will change and the cost of bitcoins could change. Say the difficulty continues on it's current trajectory (50%+ increases for simplicity) then I am going to go 0.375 to 0.1875 to 0.09375 to 0.046875 per/ day. If that happens I will never get the cost back.
I have noticed a lot of people on hear making confident predictions about difficulty increases. Ultimatley this decision hinges on the difficulty increases. So using that knowledge you lot seem to have give me your votes for option 1 or option 2!