See all the available used Mac Pros at OWC. Availablity varies over time.
The 4-core 2.66 GHz and 8-core 2.93 GHz look particularly interesting.
- The 4-core 2.66 GHz is scarcely slower than Apple’s current 2.8 GHz.
- The 2.93 GHz 8-core is a very attractive option for anyone use software that makes use of multiple cores.
- The 2.26 GHz 8-core is a solid platform for video and sound processing (for Photoshop and Lightroom and similar, stick to the faster clock speeds).
Mac Pros are workhorses generally good for years of solid use.