Assuming stock rig w/original HS non o/c @ idle (not under load) your cpu temp is perhaps a tad above optimal. Ideal is somewhere in the 37C - 54C range (recommended cpu temp
under decent load is around 43- 45C I think). Is your system stable? What are your temps under load?
You can (probably) drop your cpu temps by 5C to 8C (or better) by adding a better HSF and decent thermal compound (Arctic Silver Ceramique is getting great reviews. I will be trying it out tonight to mount a Zalman 7000Cu to a P4 2.4C). It is a little hard to say how much you can lower your cpu temp, as there are more than a couple of variables involved.
Case temps can be knocked down with fans. How many do you have in your case? Slap a vantec Tornado in that puppy.
The 80x80x25mm Tornado pushes about 84 CFM @ 5700 rpm but at a cost- it runs @ around 50+ dBa. Not exactly hair dryer loud, but…ok, you might not need a vantec, but definitely check out your case airflow. Fans that push in the 30-40CFM range @ low dBa are cheap.
The location of your system can make a difference in case temps. Is it in a desk enclosure? Exposed to sunlight? On a desk or on the floor? You are in N Texas and we are getting into the hot time of the year. I am assembling a new system in the basement and that is where it is going to stay this summer.