It's not about the size... gonna print very small only... in namecard.
The reason I'm using CMYK is becos I wanted to send it to this offset printer and they specified to use CMYK.
See
http://www.xclusive.com.sg/file.html
A lot of commercial printers would want a CMYK version of your artwork or photo for offset printing. Offset printing is basically 4 colour printing which usually means at least 4 plates are used. So each plate represent one of 4 colours to be printing over each other on the paper to form the entire colour range of your artwork or photo. Thus CMYK which stands from the name of the colour Cyan Megenta Yellow and Keyline Black. I always prepare all my artwork in that fashion too when it is to be published in magazines or promotional literature.
The reason they use this over RGB is because, CMYK has a certain colour limitation that is more suited to printing 4 colour then for you to view RGB on your monitor which can show you a wider gamut of colour range that is not possible in CMYK printing of brochure...etc. Thus printed material like brochure are a lot more limited and in some case duller.
Some printer can take your RGB and convert for you but there is the risk that their CMYK protocol selection might not be compatible between their own computer and YOURS. And if after conversion the colour are not to your liking after going to printing, imagine you getting a shock over it and rejecting it....the print shop ends up losing money over it. If after explaining to you and you don't understand what they meant by RGB to CMYK conversion issue...it will be ending badly for sure. I have seen some clients out of ignorant doing so with printers as they don't get all this colour compatibility issues. So what printer do is, they ask you to give them the file in CMYK lor. That will eliminate more then half the problem that can still crop up heheh..
This is now 2009 but unfortunately colour calibration and standards are still fragging UNSTANDARDISED. heheheh..so much for paying alot of money sometime to calibrate your monitor as I see some over zealot photographer alway seem to want to buy a calibration software heheh.. Wait till they send their photo for printing in a offset shop. heheh
okay anyway...as I said, some PC/MAC might not be using the same s/w or even the same colour space protocol to open and view your file. If you open your colour settings in Photoshop EDIT menu drop down, you can see it has a selection of RGB. CMYK and other colour space mode for you to set up Photoshop. Look at how many kind of setting there are you and can see the headache if you selected the wrong one. Telling it how to show you the colors depending on whether you open a RGB photo or CMYK..etc. THUS..... that is why when you open and do your artwork in Photoshop and then you open it with a window generic photo viewer you see that nightmare colours!!!! heheheheheh.. Because Window's own colour space for CMYK is not the same as Photoshop which is more professional and recognise by majority of the publishing standards.
But even then, there are slight differences still but very marginal (usually it would seem the colours are more duller as you start to flip from RGB to CMYK over and over again and you watch your screen closely in Photoshop) ...so any generic CMYK would be fine with printers. In general, unless you are nitpicking drama queen Art Director who insist on exactly colour representation. But they will not take RGB. As you might know as a photographer...there are at least 2 RGB standards that most use. One is more rich in color and works great for nature shoot and another which is less rich and in some cases there is the standard RGB mode you can set your DSLR to which gives you duller colours.
Most professional designer would use that as it represent a more realistic color range for printing brochure for example. RGB is more about colors that is illuminated from the rear like a typical PC monitor CRT or a LCD with the side lighting. So looking at a photo on your PC and in a magazine, you will always see more eye popping colours on your PC screen. Hope that explains things abit more... I should explain more in depth but it might confuse you further ....hope this will do for now. If you a bit blur after this...let me know..I think I might have miscue my explanation abit as I re-read it again hehe... SO REFRESH the screen in case I am still editing it for clarity.
So just convert and edit your colours in CMYK mode as the final step before you save and cast to CD and pass to them. If your monitor is not calibrated, I would further advice that you go down to the shop get them to open it on their PC/MAC and you view it again to be certain..it is as close to what you want since that would be the PC/MAC they will use to produce the colour separation for your printing ...or look like on your PC/MAC screen. ALSO, if you willing to pay abit more, usually, when the produce the colour separation, the do make colour proofs. Which you can use to preview the final print using those colour seps. When I sent out to make my own colour seps, I get a set of proof which they actually would print a simulation for my review. Welcome to the real world of desktop publishing heheheheh....