While I am not aware of the actual speed differences, I understand that the free horse moves slower in respect to the L45 one in any given zone.
There are additional benefits to having the L45 horse, including decorative addons, but especially that with Champion Levels 2-5 you get the ability to add saddlebags to the horse. They are not visible, but what they do is add 4 slots each for carrying more stuff.
You can get 2 siege weapons and a few potions on a horse with their built-in encumbrance, so thats a good reason to get them right there.
None of the higher level horses have any run speed difference amongst them, but they have different looks.
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Eggi/Sohwyn custom ui download site
BETA
http://www.4shared.com/archive/LllGqvhe/eggisohwyn1110dbeta_1_.html
(:^
I will stop procrastinating tomorrow.
DAoC desktop calender collection
http://db.tt/GnHh5Sc