Windows search vs Sisoft Sandra 2009

I have downloaded SiSoft Sandra system info and benchmarking software to test my hard drives. I ran the test and the results were very erratic! Then I stopped windows search service which was indexing files (net stop "windows search") and tried it again. The results were totally different! Now I seriously doubt that this service does not affect performance and loading times of programs and games :-\ I thought it should run with some low priority, thus pause when other other software wants to read or write to disk, but now I am not sure. Also when I check performance monitor disk I see that SearchIndexer.exe has IO priority "normal". Do I have something badly configured or this Sandra test is just not relevant to judge it?

The search indexing should stop when there is other hard drive activity like playing a game scanning for viruses etc.

Hm really valuable reply :-] You just said again what I though, but proven to be probably wrong! Did you see the pictures I attached? I tried it several times with similar result and I want some explanation. If you have and idea for some other disk speed test or benchmark, tell me. Unfortunatelly windows search indexing sometimes goes fast and sometimes slow (not much HDD activity)...