Depends on the bike. On engines that do not share the oil with the transmission, 3-5000 mile changes are often fine, or even longer in some cases.
Since this is a Kaw forum, and most Kaws DO share the engine oil with the trans, ( I can only think of the late 60's W-Series that didn't.) I'd reccommend changes in to 2-4000 mile range. the upper grade synthetics on the higher side, and conventional oils on the lower side. the Group-3's somewhere in the middle.
I tend to favor Group-3's as the higher end oil's are often too costly when you figure the extended change intervals are not long enough to justify the additional costs. Contamination from trans debris (iron) usually will not permit really long intervals, even if the viscosity holds up well. Might be for some though, as riding style has some effect on that.
Some Kaw's with the roller bearing crank/rods, such as the old Z-1/KZ1000/1100, and the KLR650 would need slightly shorter change intervals, as they tend to chew up the oil a bit more.
You will get a lot of opinions from just about everyone. Many are just speculation. The only way you can know for certain what's right for your oil choice, bike, and riding style, is to have a few oil anylisis tests done. It's not that expensive, and if you keep the bike for a long time, it's well worth it.