My 19 row fit real well. From the looks of things you can go vertical all day long (25 row, 34row.) Horizontal is a lot more cramped. I'd recommend avoiding the Setrab 9 Series 25 Row Oil Cooler. If I remember correctly it's 3 inches wider than the 6 Series.
Here's my install DIY guys, see for yourself
DIY: Oil Cooler Installation on a Nismo (Damper Included!) - vipor