If you want something fast, X5677 is a good choice as well, unless you really can utilise all 6 cores of the X5650.
Another cheap choice is the W36xx CPU. X56xx are build for dual processor system, they are more expensive then the W36xx CPU (with exactly the same core count, speed, performance).
One of the big advantage of the X56xx CPU is that they can support 64G RAM and above, but the W36xx cannot. Since your system only has 24G at this moment, W36xx may be a good choice as well.
Another cheap choice is the W36xx CPU. X56xx are build for dual processor system, they are more expensive then the W36xx CPU (with exactly the same core count, speed, performance).
One of the big advantage of the X56xx CPU is that they can support 64G RAM and above, but the W36xx cannot. Since your system only has 24G at this moment, W36xx may be a good choice as well.