A tad slower. The XPS 13 with Kaby Lake Refresh Core i5 trails the Core i7 in raw multi-core performance, but as far as overall system performance is concerned, the model with i7 is only marginally faster.
https://www.notebookcheck.net/Review-Dell-XPS-13-9360R-i5-8250U-QHD-Laptop.266690.0.html