Servers with same workload in the same rack: good, bad or unimportant?

Solution 1:

A. While it's technically true that a higher work load will consume more power and generate more heat, in a properly powered and cooled data center this shouldn't be a concern.

B. Not unless the data center is not up to snuff regarding power distribution/delivery, power protection, and cooling

Solution 2:

Ideally, you will have more than one phase available for power in each rack, so you can evenly distribute the power load over multiple legs in the same rack. You should also plan for heat removal under maximum load. While there is certainly no benefit to keeping database servers physically close to each other (assuming all other things are equal), your data center design should not limit your ability to do so. If it does, you have larger problems that could potentially manifest somewhere else down the line.