I'm in the market for wheel spacers as well..
You will definately NOT notice 5mm, in fact, I'd be surprised if you noticed 15mm..
I'm looking for 25-35 at the moment, but the cost goes up exponentially with the thickness.
If you have the standard 5-spoke 19" wheels, the bolts are long enough to put small spacers on with out lengthening them, but I don't think it's worth it unless you space them out a decent amount.
Bear in mind you will experience slightly different steering feel due the wheel offset (not dramatic) and the wear rate on the wheel bearings will increase, again, not dramatically.