upgrading my bike, Planet X Exocet to Cervelo P5

I'm fairly new to triathlon, have done 2 Olympic distances in 2 years. My bike is a Planet X Exocet 3 which was a significant upgrade to the starter bike I first got when I was trying the sport out. I am considering upgrading again and have spotted a Cervelo P5 for sale in my size which is quite unusual. The wheels on my planet X are deep rimmed Kronostok, and the Cervelo has Zipp 808s also in deep rim. Both bikes are di2 so no upgrade there. The price premium on the Cervelo is about £1,300 (assuming I sold the Planet X for the same price I got it). I've no doubt the Cervelo is the superior bike, but my concern is that I could be paying a lot of money for what could be a marginal gain. So does anyone have any experience with these models and how much better one is over the other?