5x5 is an ambitious embark size. If you have a long world history, and aren't running with any of the fps boosters enabled... yeah. Flowing water and especially magma with temperature enabled can also be a drag. Waterfalls, too. Also, if your map is especially deep (lots of z-levels, perhaps if you've required many solid layers between each cavern layer or above the magma sea), that definitely has an impact.
Have you run the PAE enabler executable on your Dwarf Fortress.exe? If not, the vast majority of your RAM isn't helping you at all, and your video card doesn't help much in any case. Dwarf Fortress is a very processor-limited game. Your processor's not weak by any stretch, but again, your embark size is quite ambitious. Try 4x5 or 4x4. I run 3x3 typically, but I'm on an i5 laptop that's a couple revisions behind, so that's probably not necessary for you. Decreasing the length of your world history can also help, but young worlds are somewhat impoverished (dragons won't grow to full size with fewer than 1000 years of history - but honestly good luck getting a playable civ to live 1000 years anyway.)
