Claire was 2.9kg/6lb 7oz and 48cm long when born. She wore 00000 for about 6 - 8 weeks, and then wore 0000 until about 2.5 - 3 months. She is now 4 months and in 000.
People told me the same thing - not to get any 00000 and 0000 clothes, but we definately used them for long enough to get some worth from them.
We got a bunch of those all in one suits - great because they dont ride up at the back like a two piece outfir does, and I do agree that the envelope neck or the ones with the studs to open the neck up are so much easier.