Source Unpack Game Lag


I’ve been playing around with Portal lately and I downloaded the 5135 version from the Source Unpack to play with oob. The problem is that it will run at ~6-7 fps at lowest settings and 640x480 resolution. The steam version of the game runs fine (70 - 80 fps) at 1600x900. Is there something I am missing or am I just using a bad computer?

Specs -

CPU - Intel i5 25k
Graphics Card - Nvidia GForce GT 730


I usually disable multi-core rendering and turn the affinity down to just 1-2 cores. This helps solve all my lag issues.