of course you can keep growth going. but you would need to stop at 39 or whatever and then pay out dividends to everyone like you promised. i would recommend sticking to your original gameplan b/c by my estimation this is what you promised to do and no one can argue with that. once everyones paid off then you can re-enter your growth phase with more rigs. the skys the limit as far as i'm concerned with btc related businesses. don't forget we'll all be holding shares which should go UP if you play your cards right even if you are just paying dividends. that would be a source of income to grow your rig count as well.
The original number of 39 rigs was just used to give numbers should the IPO completely sell. That number of rigs was calculated at about $7.40 per BTC, so if the IPO sold out right now we'd have quite a bit more. It wasn't really a promise, just a number used to calculate output and payouts. Also, how do you know when everyone is paid off? Some people will be receiving dividends for longer because they bought in sooner, etc.
I would suggest calculating a USD per 100MH/s rate above which it is more profitable to sell mined BTC (and expand business) and below which it might pay off more to keep (or pay out) BTC to investors, since they are not very profitable to be sold anyways.
Currently 100 MH/s net over 4 USD/day, so I would advise on selling the mined BTC for USD as fast as possible. After the difficulty increase this will very likely melt down very fast, so it might be more wise to keep them.
In the end I wnat you do do something like in this thread:
http://forum.bitcoin.org/index.php?topic=7427.0I did a calculation based on 1000 MH/s because I know how roughly how much power is consumed by that figure, and the price of BTC needs to drop to about $1.30 for mining to get close to being unprofitable. It would need to go down to $8.00 at a capacity of 7GH/s to disallow for a single rig to be purchased a week. I'm not sure at what threshold you would consider it less profitable to sell the BTC and to pay them out as dividends instead. As far as the graphs, I don't really have the time to, however I would not be against a motion to pay sharp to do something of the like.