Kenneth,
While one might guess that IndexSeek would be faster than Seek, that is not the value of IndexSeek. If you are using Record buffering and you move the record pointer there is an implicit tableupdate fired. If you want to find out if there is another record with a certain value in the index on the same table, then you are locked into either using Table buffering, or opening the same table twice under different alias'. Unless you use IndexSeek to do the look up. Since IndexSeek only tranverse the index and does not move the recor dpointer it does not cause an implicit TableUpdate to occur.
The point is that when you need IndexSeek to accomplish a task, the issue of speed is much less important. Only IndexSeek can do what it does.