I don't think this is a wise approach. It will only tell you what that specific copier can produce in it's current state. When you get a new one, it will have it's own calibration, and will produce much different colors. And will you be getting a Fiery controller?
Also, when you receive files in the real world from customers, I doubt you will spend the time to go and convert each one to the CMYK values. Besides, you will get much better results if you leave it as the PMS color. If the MFP or digital press has a Fiery controller, you can go into the spot colors section, open the Pantone color you are targeting, print out a sheet of color patches, and pick which one matches the pantone book. If you convert to CMYK, you lose this capability. Also, if you do this process, are you going to be present when they do it? Are you going to expect them to just print it and not allow them to make any adjustments? What profile do you want them to use?
Instead, I would bring a series of your real world files along with your own media and ask each vendor to print while you are present...or if you sorta know what you're doing, then let you print while they 'supervise'. This will allow you to see how the machine really works when changing out different weights and textures of media. Bring some coated and uncoated media, some lightly textured and heavily textured media, bring some synthetics, envelopes etc. Make sure you bring some files with heavy solids, files with gradients, files that had transparency issues, and files with skin tones. And yes, bring some with a pantone color, still in pantone mode, not CMYK. Let them show you how you can match on the fly. If they can't show you, then don't go with that vendor because they probably don't have good training/support locally.
If you have specific finishing needs like booklet making, time how long it takes on each press. Some machines really slow down on the finishing.
Do you run jobs with mixed media? Bring those kinds of jobs and the paper. (Don't assume they will have all of the stocks you run). Some presses slow down significantly when switching between media, while others switch without missing a beat.
Lastly, I would recommend printing a large amount of one specific file that has lots of solids and images to see how the press runs continually...something like 500-1,000 sheets. This will show you 2 things: How often the press has to stop and make adjustments, and if the print is consistent from sheet 1 to sheet 1,000. Make sure you time how long the run takes and repeat the exact same process at each vendor. They will sweat a little when you bring out the stop watch, knowing they are seriously up against the competition. This will also encourage them to give you their best pricing.
This all may sound like alot, but if you're going to make such a big investment, you should really put it through some serious tests, and not just 1 sheet of pantone colors that you may never even use.
