Gramps,
Yeah, you can.
What I'd do, if I were you, would be to take all of my largest flies, the size 1/0 streamers, the spun deer hair bass bugs, the clousers, etc., down to the local pond/lake/or lawn at the park.
Put a reasonably stout leader/tippet on your 3 wt.. The same set up, at least, leader/tippet wise you'd use for the same flies on a 6 wt.
See how each casts for 'you'.
You will be surprised, I guarantee it, by what you can actually cast with a lighter rod. You'll also get some idea of what kind of distance limitations this type of casting will entail (it is a trade off, unfortunetly. The lighter line can colaspe at longer distances with heavier and more wind resistant flies). Different for each, as skill plays a part here.
Just try it.
Good Luck!
Buddy
It Just Doesn't Matter....