I am using iPhone 4 with stock firmware 4.0

Can I use the jailbreakme.com method with this firmware or do I have to upgrade to 4.0.1?

I have read several problems with 4.0.1 being a bit slower, or buggy, or even draining more battery. My phone has been working fine now and don't see any reason to upgrade firmware, unless I have to do jailbreak.

So do I gotta upgrade or will I be safe at 4.0? Gotta find out before apple throws the new firmware out and screws me.