So as it currently stands, do you have to join a group to have any chance of being the first to encrypt a block? Is it possible for a single rig to even mint a block in time?
depends on your power. with two 5970 - probably mining solo is better. if you have single card - probably it will be the best to join pool. this way you will see you reward constantly (but probably less in total if you mine solo in the long-long run).
and pools are also nice 'cos you do not need to setup local bitcoin server. you even do not need to use it and withdraw coins directly to some exchanger lol (but I do not suggest to simplify process so much) =))