For information purposes: We used a variation of my propossed mounted combat. We assume all the mounted people made their horse combat rolls at exactly 1/2 of allowed rolls, all for knights, just base and spec for cavalry. So adding that value for lance/spear charges, or versus foot targets. It seemed to work quite well. All where impressed with the resulting feel of mounted advantage.
Sounds like a good rule, and I'm glad ERP is easily customized without as much of a cascading effect, like you'd find in other systems.