I think the important information is - what are you using them for? TT, Tri, or both? Is there likely to be any need to be UCI legal?
My instinct is that they’re both fast bikes, so unless there’s some feature on the Giant that you really think you need (or some feature of the P5 you need to be rid of), it’s not going to give you any particular gains over the P5. You’re more likely to find gains with helmet, skinsuit, position, maybe a new set of bars.