[a humble lich]

I'm trying to think of RPGs from the roughly same time as when the GURPS magic and psionics systems were being developed. In most of them treated magic and psi very differently, although I can't think of too many which had both magic and psi. In both 1st and 2nd edition of AD&D, psioncis were very different from the magic system. In 1st edition, psi were just special powers that your character might randomly have, and in 2nd edition there was a psionisist class, but the system was radically different from the Cleric or Wizard spell casting system. The Paladium RPGs (Rifts, Paladium Fantasy, and Beyond the Supernatural) also had a psi system which differed a fair amount from the magic system

In contrast, I remember the Rolemaster games and the games from Bard Press (Atlantis and Talislanta) having "mentalist" classes which were basically just another type of magic user.

Also, I'd like to give a warning that the 3rd edition Psionics rules had some balance issues. I personally like the general design of 3rd edition Psionics, but points-wise they are much cheaper than 4th edition.