As pointed out in D2585, basic, advanced, elite, champion, and hero cavalry all have somewhat different walk speed multiplliers, which is confusing and makes comparing and tweaking slightly harder. The values were last changed in D930/rP20230, which replaced absolute movement speed values with relative multipliers.
There is no clear reason why champion cavalry ought to be faster than their citizen counterparts; they have more attack, armour, and health and can't gather, so I'd expect them to be slower rather than faster.
This patch standardizes the walk speed multipliers for all cavalry (to ×2.0, which is nicely rounded in between ×1.85, ×1.95, ×2.25). For comparison, all cavalry benefit equally from the two speed technologies (10% each) and various auras.
As a consequence, mixed cavalry groups (a hero with some champions and citizens) would easier stay together on raids. And yes, cavalry spearmen can still catch ranged cavalry; higher level template modifications are not changed.