You may want to look into SSD storage. For example, this product promises 6 GB/Sec of bandwidth on a 5 TB device. http://www.fusionio.com/products/iodriveoctal
With 10 units, you would have 60 GB/Sec of IO bandwidth with 50 TB of storage. That would be enough bandwidth to let you read 50 TB in about 14 minutes.
Of course you may want to verify that the vendors product can actually do what they claim. :-)
There are plenty of other potential bottlenecks when you get into this area: PCI bus speed, memory speed, front-side bus speed, processor speed, etc. I think you will find this a difficult challenge with current hardware.
I would recommend waiting as long as possible to buy the hardware, instead of trying to buy something now that will be good for three years. Performance of hardware per dollar will be much better later, especially for emerging technology like SSD storage.
I would also look into database compression if you are not already using it. If you can get 70% compression that will save a lot of space and IO bandwidth. Use it with partitioned tables to tailor compression for best performance, like compressing anything older than 90 days. Even though it uses more CPU, you save a lot on IO and memory footprint.
Also, I would seriously explore the importance of this to the business. It is easy to demand fantastic performance when you don't understand the cost, but when you start talking millions of dollars people will take a harder look at the value they are getting for that money. Perhaps a solution where they could see all the recent data quickly would be enough. Or you might be able to break the most important data out to a smaller dataset that doesn't require as much time to query.