XP era spanned a long time. Core 2 Duo was released near the end of that so pretty much peak XP performance. Early XP with Pentium 3 and 4, not so much. Something like a Core 2 Duo E8400 or Core 2 Quad Q9550 actually handled Windows 7 very well particularly if one pairs it with an SSD. Moreso with a discrete GPU for Aero.
A large part of the SSD push actually came about because Intel processors were fast enough that the storage subsystem became the biggest bottleneck for most people's usage. If one has a PC with HDD from 2011, installing an SSD on it is like a breath of fresh air. I bought my first SSD in 2009, iirc. By 2011, all my computers had at least a 120GB SSD for operating system and programs. Power efficiency became a bigger focus for Intel rather than pure performance. I had low-power 1.8GHz Celeron 1037U Ivy Bridge Mini-ITX builds with 128GB SSD on Windows 7 handling basic computing duties just fine.
I don't have extensive experience with Windows 10 but the few laptops I've dealt wih (ULV processors so likely still slower than Core i5-2500) don't appear to run significantly slower than Windows 7, again, as long as the build has a decent SSD and at least 4GB RAM.
P.S. Just checked PassMark. A Core 2 Duo E8400 actually scores higher in single-core than the Core M-5Y31 found in some rMB and ultrabooks.