Most printers prefer CMYK because that is how the plates are run. If it creates a huge color deference in the image you might want to bump up the contrast a bit. Blues and purples, and greens tend to change the most with the color shift.
You really need to be in constant contact with your printers. They will advise you about color conversions and in what format they need you to send the files they are to print. If you are talking about ink on paper you will definitely need a CMYK file somewhere down the line. Some printers will do the conversion for you if you are not comfortable doing it yourself but you will need to take a look at their results. The brightest, most saturated colors may shift and look a little duller than what you see on your monitor when viewing an RGB image. If at all possible, be there when they are printing your job. If you cannot be there, ask them to make sure someone with color knowledge is at the printing.
RGB can sometimes be difficult to predict the end result when printing CMYK.
I always like to refer to a CMYK colour chart, it is easiest for colour reference, ask your printer for one. If you want the sky in a photo to print a bright blue, then you can refer to the colour chart to see what the result of the CMYK breakdown will print like.
You can then edit / adjust the levels and curves in photoshop to get a more accurate end result.
Color management is for closed workflows. In other words, I can control the colour from MY camera, to MY monitor to MY printer. For the most part at least. By applying one color profile to all output devices I can see a fairly uniform color from start to finish. When dealing with outside printers and output, don't bother.
I do consulting in the print industry since I've been doing prepress since god first contemplated creating a universe and I get calls from printers regarding color a lot. I got a call from a printer once in which they had been trying for 4 hours to match color on press to a digital proof made from a supplied PDF. It took me 3 minutes on the phone with the guy. I asked, what color profile is embedded in the PDF? Uh, I dunno. OK, How about this: what color profile are you using in your workflow? let me get back to you. Turns out the supplied PDF had a different color profile then the RIP making the plates. They had the client send a new PDF without color management and voila, the color matched. Color management is idiotic.
As for the original question: I've said it before and I'll say it again. There is no such thing as an RGB press. That means that all elements, images or otherwise, have to be converted to process (CMYK) prior to printing. If your printer will do it for you at no extra cost, let them. Be aware that the CMYK gamut is smaller than RGB (range of colors) so some shifting will occur. This is inevitable. Shoot for pleasing color and you won't have an aneurysm.
Also, technical thing but Pantone is not a color space. It's a collection of special premixed inks used to reproduce precise colors, many outside the CMYK gamut.
Macro USM, Sigma OS 70-200mm f/2.8 EX DG HSM, Sigma 2X Tele-converter...
I was reading some of the answers to the question you asked. I am more confused then when I started reading. Jonnycwh if you are going to send a project to be printed on an Offset press the files will need to be in a CMYK format if they are sent in an RGB format any printer or prepress department is going to call you and inform you that the files are incorrect. I have worked in printing for almost 30 years now and seen many awesome changes in the field but somethings have to be done a certain way and thats it for now.
I can guarantee that if i had a color problem the last person I am going to call is a photographer to tell me how ro get the print quality up to par on my four and 6 color presses.
Please contact your preferred printer and let them tell you which format they want you to send the files in, a real quality shop will want both the Press quality pdf as well as the native files in case there are any issues with the files. A good quality printing company will be certified in color management and will have the press and platesetters calibrated to each other so what is on the plate will be what is on paper. I also agree if possible be there for a press check if the job is that critical.
Speak to your printers and find out what they want but I would suggest that they will ask for CMYK. As others have said here you would need to tweak the colours after converting to that colour space as after the conversion it will be a lot duller.
Also make sure that you get a proof to sign off on that they print for you and don't be afraid to go back at them if you are not happy with it or there is a problem with the colours (as there often is!). Otherwise if there is an issue and you flag it after they have done the print run it would be like banging your head off a brick wall to get it rectified. You have also then covered yourself if the print run does not come up to par with the proof they supplied you with. Some printers will try to email it to you in a pdf format but I always insist on having it in my hands on paper as what you see on screen is rarely the end result.
I hope this helps!
100mm Macro L
Canon 85mm F1.8
Tamron 70-200 F2.8 IS