Hey Portman,
Happy to hear from Remo and other day-traders on the numbers, but for now, having checked IG Markets this morning, the day's high I have is
6700.4.
Now, all things said, IG do in their capacity as book-makers and synthetic market-markers, can and do work with their own figures.
They, like other providers, do stipulate that they use underlying data, but they never state that is it 100%. Giving themselves this flexibility means that they can - allegedly - control a lot of trades, and scoop lots of stops (just a "follow-the-money theory).
Good luck!
Edit: Doh! Just noticed Remo has replied!
Edit two: Thomson Reuters Eikon shows 6,695.92. I'd take that over IG any time