Doing more upper division class work before transfer?

I am transferring from inside UC, aiming at Berkeley. I wonder if it is wise to take advantage of the research universities UCs are and manage to take some upper division courses early on. Often, upper division classes are the ones that actually interest me anyway.

I am likely a humanities major, so prerequisite is not a problem for many upper division classes. As for the alternative of doing honor classes, I did not enter as an honor student, and departmental honor also seems not for those who intend to transfer.

If AP/IB are well-received in college entry, wouldn’t the rigor of college class be considered even more significant? I think it can make me look more research-oriented and academically curious. Do you guys think that is a good move? Is it even doable in your experience?