It takes my FRED approximately 105 minutes to acquire an 80GB hard drive image without compression and another 30 minutes to validate it.
That is quite slow for modern day hardware. On a consumer-range hardware with (e)SATA-2 using a linear acquiry tool (EnCase/linen/ewfacquire) you should be able to image a 80GB HD in roughly 30 minutes without compression. But note that the performance will also be dependent on the reading speed of the source disk and writing speed of the target disk.
The performance impact of the compression will be dependent on the power of the CPU and the memory-bus speed.
Some old test figures of mine on a slow 40GB HD imaging on consumer-range hardware
33 MB/s no compression
18 MB/s best compression
29 MB/s best compression on 2 cores.
In the right circumstances empty-block and fast compression can be even faster than no compression on 2 cores. Roughly 37 MB/s no compression vs. 43 MB/s fast compression.
Note that the bottlenecks highly depend on the imaging solution and the source disks.