Good bare-bone or industrial PC to run ROS.

edit

As you're phrased it, this is a question with many very subjective answers. There are so many good industrial PCs out there that it's hard to make any recommendation.

• Realtime performance (the ability to run recurring tasks at precise intervals or respond to incoming events with low latency) comes from the operating system and your software, not the hardware. RT means something different to everyone, so it's basically useless as a requirement. Instead, I suggest you define the timing requirements that you need in order for your software to run successfully.
• GUI and CV are also very subjective. If you have a sample version of your application, I suggest you benchmark it on a desktop CPU from a similar manufacturer, and measure the algorithm's runtime, cycle time and overall CPU usage. From there, you should be able to multiply the test CPU's speed by the CPU usage to determine how fast your final CPU needs to be. Add 10-50% to give yourself some margin for error and some room for your software to grow and change.
• Perform a similar analysis for memory usage. RAM is generally cheap, so it's easy to give yourself plenty of overhead.
• If you don't have something that is already written, try to find a similar project, and benchmark it.
• Consider if you will be operating in a high-temperature or high-vibration environment. This generally requires computers that are built to withstand these conditions.
• Consider if your computer will be running for extended periods of time or in a safety-critical system. If either of these is true, you probably need ECC memory.

Once you have answers to all of these question, you'll have a rough estimate of the number of CPU cores, clock speed, memory, and other requirements. This will help you narrow in on the industrial computer that fits your needs.

If you don't have or can't get answers for these, I'd suggest a computer with a high clock speed and plenty of RAM. Research applications tend to be largely single-threaded and do well on a CPU with good single-threaded performance.