My post never slipped or creaked luckily enough........I'm 18st too
Hmm, I think the fact that some have Seat Posts, BB, Cables etc that creak/rattle + slip for some but, not for others who have the exact same components, is a clear indication of the inconsistencies that exist within the quality control area of more than just one manufacturer.
Sorry if that sounded a bit ranty but, after doing your research and 'more importantly' saving up your hard earned cash, the last thing you want is to feel dissapointed with your proud new purchase