The payout system is Proportional. We do not auto-convert to BTC. You can auto-sell the coins on Cryptsy that you don't want to hold in your personal wallet(s).
Auto payout is done every 5 minutes. You can set your auto-payout thresholds as low as 1 coin.
About that, what formula does the "Proportional scoring" uses?
Thanks!
Proportional means that your payout is proportional to the number of shares you submitted. If you submitted 100 shares and the block took the pool 10000 shares as a whole then your payout would be 1% of that block.