I don't know if this will work for anybody, but it worked for me. I installed Vindictus on my old laptop (so I can carry it whenever I go somewhere non-education-related), and I really lagged worse than I predicted. It was giving me 1-5 FPS. I was using IOBit's Game Booster too.
So I thought, "That's strange. With this laptop's spec, I should be able to get higher FPS." So, I toned down the graphic settings, didn't help much. After muddling around, I decided to go to Task Manager and look at the Process tab. Vindictus didn't take much RAM, so I figured it was processor-related. The laptop is using a dual-core processor motherboard.
Set Affinity to only 1 core, and the FPS went up by like... 15-20. So now it hovers around 15-30, non-town areas. I think devCAT didn't update the game's Source engine to optimize for multi-core processing. So if you're having some bad graphical lag on a low-spec computer that is multi-core, try setting the process (vindictus.exe) to one core.