Comment Nope, 4" is more than enough (Score 3, Informative) 377
With my 70mm (2.75") telescope, I can see Saturn's rings more clearly than either of those photos, and 2 cloud bands on Jupiter. What'll influence how well you can see them more than the diameter of your lens is the focal lengths of your telescope and eyepiece and the quality of the lenses. My scope has a 600mm focal length, so with my 9mm eyepiece, I get about 67x magnification (600/9). I have a 2x barlow, which makes the image bigger, but it's not very good quality, so it blurs it so much that it's not worth using.
I'd recommend Jupiter, Saturn, the Orion Nebula and the Pleiades. They're all super easy to locate once you know where to look (you can see them all with the naked eye...just not very well!). Also, definitely get a good look at the moon. It's more interesting when it's not full, since that gives you more relief. Unless you have a filter, with a 4" main lens, the moon is going to be pretty bright.
I'd recommend Jupiter, Saturn, the Orion Nebula and the Pleiades. They're all super easy to locate once you know where to look (you can see them all with the naked eye...just not very well!). Also, definitely get a good look at the moon. It's more interesting when it's not full, since that gives you more relief. Unless you have a filter, with a 4" main lens, the moon is going to be pretty bright.