Lighter wheels; I'm running carbon but forged alloys not far off weight wise and cheaper. Lighter exhaust saves you a bit; ditches the exhaust servo box too which is weighty. Carbon body work; subframe, tank etc. Expensive again but saves a few kg. LiPo battery saves about 1.5kg and is the cheapest £ to kg weight/cost ratio I've done so far. It all depends how far down the £/kg rabbit hole you want to go?
