I've gone to 7,000 mile intervals. There's no difference in oils as far as I know. I contacted Suzuki Customer Services and asked what the changes were and got a reply saying they didn't know as the factory doesn't tell them so I best stick to 4000 intervals
I replied saying that was basically bollocks...
I do change my oil/filter around 6 months though (c.4,000 miles) mainly after winter as it was getting milky. If that problem doesn't occur this winter (think it was breather sponge being stuffed in blocking hole) I'll not bother.