There are many reason why your system can BOG down during recording and playback of Logic

Here's a few tips for Optimal performance

1) When recording lower the buffer size of your Audio card as low as the card will allow so that you can achieve the best latency results
2) When playing back - increase the buffer size for maximum playback power from the CPU
3) Allocate as much RAM to the host program as you can but also allocate RAM to the other products that you may be using as in SOFTsynths like EXS24, REason and so on...
4) cut down the track count that you are using per song. In other words, if you are only using 12 Audio tracks, then do't have your Audio driver enable 24 Audio tracks. Eachof those unused tracks takes up resources from your computer/ You can find this in the audio hardware and drivers section of Audio directory.
5) learn to use your AUX buses within the MIXER window for your stonger effects like reverbs and compressors henceforth taking more pressure off the CPU