I'm going to post this again here, as I feel people have some misconceptions about solo-mining and how long it should take to find a block:
More realistically than trying to anticipate a time frame to find a block (because by nature that is impossible due to probability), is to look at every block that's found.
At this moment, with 10 TH/s you have approximately a 1 in 46,338 chance of holding the magic hash every time a block is found. Those odds do not lower at every block as the calculators would have you believe, they are the same odds every time (until difficulty is adjusted, and personally I would plan for a ~3% average difficulty increase between now and the halving)
You could have a 1 MH/s miner and the first hash that goes out is the winner, or likewise you could have 1 PH/s and go weeks without a block. Do yourself a favour and look at some of the medium-sized pools (like Eligius for example) and look at the block history and their luck. The variance is huge, and they are operating with 14 PH/s. For you to solve 1 block within 300 days would require flat difficulty and >100% luck in comparison. Imagine how it would play out if "your" block was a 25% luck block (you would have to mine for ~3.25 years with your hashrate keeping up with difficulty if that was the case).
I hope this makes sense.
And as far as what you said about finding blocks in the pool, when you are in a true pool and not solo-mining, you don't have to be the one to find the block. Payment is handed out based on the work your miners performed in order to eliminate the variance that exists when solo-mining. Therefore in a pool, hash-rate is hash-rate, the more you have the more you earn, your hashrate will not have any perceivable impact on the pool's performance of finding blocks.
Also, you will need a larger than 350W PSU to power S3's. Realistically with ATX PSU's, you don't want to load them over 80-85% for efficiency and durability (at least in my experience). And even then at sustained loads that high with warm ambient temperature, you will see failures especially with lower quality PSU's. I would suggest >400W PSU's for standard S3's, and >450W PSU's for S3+'s. If you have access to 240V, PSU's like those in my signature can save you a lot of money, as each 2880W PSU can power 8x S3 or S3+'s.