That was basically the gist of my question, and I'd be interested to hear more opinions on the matter. At the thread below you will find a similar discussion. I found another thread like it at one point but I can't find it now. The answers varied pretty much between 9 and 10 feet.
There is, of course, the ones that have beaks, like the Golite Hut 1 and 2, and the Spinnshelter. I also hear that Granite Gear is coming out with a new tarp with beaks.
I thought I'd give an update on the original topic. I started comparing the area of the Oware 2 and the SpinnTwinn and it became clear to me that it isn't an apples to apples comparison. Really, the SpinnTwinn gives as much area as the Oware CatTarp 3.0. Just something to consider if you want to fit two people plus gear.
I actually chose the Granite Gear White Lightnin'. The reason was mostly cost (I found one for $90). It is a little heavy, but it seems better suited to a beginner, with the adjustable tie-outs and tension tape. I got the small size, which is 8 feet by 10 feet. It is not catenary cut but I thought the tape would make it so that I can pull it very taut. Plus, it is made of Sil Cordura, which I've heard is more durable. If anyone is interested I may give a user review after I've used it for a while. I did try to pitch it today and it didn't go quite as well as I had hoped but it was my first experience, I didn't have much time, and I didn't have good poles to use. I think it will work out well with time.
Mostly I wanted a bigger tarp because I want to fit two people at times, and I didn't want the extra cost of a bivy. If I knew I were going solo and I had tons of cash I'd go with a bivy and a small tarp probably (integrated bug protection). But that is much heavier unless you spend a lot of money.