IMO, unless the temp run so hot that you begin to have lock ups (which won't happen under 80°C I think), you won't have performance differences if you run at 35° C or 70° C. However, the life expectancy of your CPU will probably be seriously shortened if you run above the 60s. I try to stay ideally under the 40s (hard to achieve with a AMD 64), with 50°C as hard ceiling.
Ideally your MB should be ~10°C cooler than the CPU. It looks like your doing fine now.