Angelo, most any weight fly rod will cast a range of fly sizes, and even some much larger than you might expect. For example, I've cast flies tied on 2/0 hooks, even poppers with my 6 wt. However, doing so limits how far I can effectively cast. It's not something I would do normally, but it can be done.
The weight & wind resistance will have an affect on how well & how far you can cast the larger flies too. For example, casting a #4 Gray Ghost streamer will be easier than casting a #4 popper. Your skill level & other variables like wind will also have some effect.
You should be able to catch plenty of bass if you can at least cast the larger flies 30-40 ft. Beyond that range it will be more difficult to cast & to control the line & fly. I've found that I catch most fish within that range anyway, so rarely have the need to cast further than that.
I agree with greased line swinger, a leader about 6-7 ft should work fine, but the larger in fly size you go, the heavier the tippet you should be using. Although I do use straight leaders sometimes, I think you might do better with a tapered leader, even if it's only two sections. If you limit your largest fly size to a #4, you should be fine with a leader that has about a 10 lb tippet for bass. As you go smaller with the flies, a slightly smaller tippet might be fine too, like down to about 8 lb test. Bass are not usually line shy anyway.
If you try the single size leader, try something like 15 lb test. You won't need it for the fish usually, but might to have enough stiffness to turn over the fly properly. Use a loop knot to attach your fly, which will give you the most fly movement with the heavier tippets.
Let us know how it works out for you. Pictures of some bass would be nice too!
