The Sportage will be on the very top end. It’s the Tucson underneath, which currently tops out at £5600, but has additional equipment and is positioned more in the “premium segment”. If it follows logic (i know it doesn’t, but assumed it does) my guess would be £6500 for the Sportage GT Line S PHEV. If the PHEV comes to the scheme in the first place, it’s not yet available anyway and the Tucson similarly wasn’t available initially as the PHEV.
It’s basically a Tucson + the £1500 optional tech pack (which is standard in the Kia).
No idea about the C5X though. My guess would be that in top spec it tops out at around £4500-£5000, judging by the C5 Aircross price.