top speed in 4 wheel drive?

Hey, I have an '89 cherokee and haven't done much offroading or such yet, well I'm going over the pass today and want to know how fast I can take it in 4H. I was thinking around 45-50, but please advise!

I should have asked sooner, but I'm leaving fairly in about 15 minutes...

There's no technical top limit, except for the fairly obvious "if you need 4WD you shouldn't be going all that fast" rule.