Rams horn manifold question

[70Custom10Nut]

Do the factory Rams Horn manifolds come in different sizes? How well do they flow? I've seen them called "Rams horn Headers", but they all look about the same. My engine is a little warmer than stock, so I don't need super hi flow headers. Actually, I'm beginning to think the lack of back pressure in my system (shorty headers into 2 1/2 inch tube and mini turbo muffs) is causing the hesitation I have.
Reason I ask is I can get a pair for next to nothing, and as another board member said, it does away with the constant gasket failure on a header setup. Cnut