Only you can be the judge of that. It's going to depend on a lot of factors not least the weather, and how motivated and disciplined you are.
One sees many fair-weather types stringing tarps of about that size up high with long guys in order to gain a bit of headroom whilst saving on weight and bulk. That's all well and good for a gentle vertical shower devoid of wind that isn't going to last long, but for any serious use pitching like that is more about a psychological comfort of having a roof and perhaps as more as a parasol kind of thing than any serious weather protection.
Take a peek at the pic below. I seldom use a lid that size because it is too inconvenient but on a whim I did a couple of nights out under it just to keep me in touch with mah retro roots. That configuration uses a poncho about the size you mention, and it is the most weatherproof way of doing it. What you should note:
1] I am longer than 6' so I have very little beyond my head and feet. Unless the rain is vertical or comes exactly side on and the wind doesn't change something is going to get wet.
2] The apex is only about 2' from the floor. When you consider the geometry and how little useful room there is at the apex, say compared to a dome shape, the effective usable height is much lower. In fact, the apex is only really useful for allowing you a tiny bit of wiggle room to load into the sleeping bag inside.
3] There is almost no room for gear.
4] Cooking under one is a pain.
5] What you can't see from that pick is that I use it in conjunction with a bivvy bag. Not only does that nerf the water ingress problems but also I can shuffle the foot end out and drag mah pack in to close the head of the tarp. It's also the solution to making coffee and breakfast which you might not necessarily want to get up to do, especially if it is raining.
