Setting up a PSC option E for design and trying to decide on the best way to control the programme and cost as the works are time critical yet not well defined. Are their any contractual mechanisms I can use?
Thinking of using sectional completion (or key dates) tied to deliverables, with X6 (early completion) and X7 (delayed damages). Or X20 KPIs to incentivize budget and/or forecast compliance.
It sounds like you have already considered the appropriate contract mechanisms, which are usually best used by applying a mix of incentives and disincentives, rather than just focusing on one or the other.
Personally I would also suggest that you don’t implement an 'all or nothing ’ approach and instead apply these as a series of ‘targets’, such as design stages or even sub dividing these. If a ‘target’ is missed then there are future opportunities to achieve an incentive, which facilitates a positive attitude and approach throughout the project, even where a ‘target’ is not achieved early in the programme.