The 75GXP has a storage capacity of 75 GB and the 60GXP can only go up to 60 GB.  Both are 7200 rpm drives and have the Ultra ATA/100 interface.  They also have an ave. seek time of 8.5 ms.  Here's where they differ slightly.  The 70 GXP is faster with a sustained transfer rate of 37 MB/sec compared to 40 MB/sec for the 60GXP.  Not too bad there.