The defaults for these 2 parameters are terrible for OLTP systems which are the most common type of database. They lead to more full table scans and bad queries. Generally you want to set these parameters BEFORE you go live. You do it in the test phase.
If you change them after you go live then you risk change other queries that were tuned to bad settings. It sounds like you do not know alot about database tuning since you mention response time instead of query plans. You should not touch these parameters.
Most DBAs don't grasp the difference in concepts between fix and design. After you are live, you are fixing and that is when you need to be careful changing these parameters. Before you go live in you are in design and development phase. That is when you adjust parameters like this.
BTW, a good place to start with these parameters (note BEFORE YOU GO TO PRODUCITON AND ONLY IF YOU KNOW WHAT YOU ARE DOING!)
This is for OLTPs. For batch processing the settings you want to start with are very different. I tinker with these a little, but those settings give me the best overall results 99% of the time on an OLTP. However, I do NOT touch them after we go to production. If they are bad, I leave them bad and tune the queries.