Honestly, you don't need to be high level at all if you are a cav. 90% of your work is done by the horse who isn't determined by your level (yeah the requirement but well, 5 is enough). Furthermore, on horse you don't care about equipment weight. So you can wear plate at low level. You don't even care about swing speed, as the slower you swing, the easier the timing gets and you get more speed bonus (iirc slower swing speed means more speed bonus on horse, as unlogical as it sounds).
This all implies you stay on your horse but meh, you have a monsterhorse and will likely die before him even with heavy armor.
