I do write apps and more and no longer will consider the slower drives. In fact I changed out the slow 5400 for a this -> http://www.amazon.com/Seagate-Momentus-Solid-Hybrid-ST95005620AS/dp/B003NSBF32
Much faster. You claim you will work with 10GB datasets so the HDD speed becomes more important than the CPU. I could make bet that a Core2duo with that drive could outperform a new i5 machine with the usual 5400 drive when it came to 10GB datasets.
It's not the programming, it's the application that would matter here. When I write my program it's actually very easy to use my older Core2duo with 4GB RAM and slow HDD.