The Steam store listing for Middle-earth: Shadow of Mordor have shed some light on the system requirements for the PC version of the game.
Minimum
OS: 64-bit: Vista, Win 7, Win 8
Processor: Intel Core i5-750, 2.67 GHz | AMD Phenom II X4 965, 3.4 GHz
Memory: 4 GB RAM
Graphics: NVIDIA GeForce GTX 560 | AMD Radeon HD 6950
DirectX: Version 11
Network: Broadband Internet connection
Hard Drive: 25 GB available space

Recommended
OS: 64-bit: Win 7, Win 8
Processor: Intel Core i7-3770, 3.4 GHz | AMD FX-8350, 4.0 GHz
Memory: 8 GB RAM
Graphics: NVIDIA GeForce GTX 670 | AMD Radeon HD 7970
DirectX: Version 11
Network: Broadband Internet connection
Hard Drive: 40 GB available space

It now seems as though I'm going to need a new CPU and as such, a new motherboard, in addition to a new hard drive just to accommodate these new releases.

As announced a few days back, Shadow of Mordor will be released on October 7.