MacBench's CPU test is influenced by cache speeds far more than real world applications. In my tests last year with a utility that would toggle these modes on an Apple G3, I saw very little gain from Write-back mode, at least in the Apple G3. Perhaps with the 66-100MHz memory bus speeds it's less of a performance issue than with older Macs that have a much slower memory bus. Gauge Pro Utility Note the CPU stepping of the review sample was an early one - v2.2. Shipping models may be a later revision.
Many readers frequently ask if a specific C reading is too high.
Most commercial CPUs are rated for 65C operation and if you have a temperature problem you'll know it quickly in my experience - as errors in the OS will occur almost immediately when a CPU overheats. Bottom Line is that if your CPU is running too hot the Mac OS will let you know very quickly. What's interesting is that Apple's G4 Sawtooth system seems to have speculative processing disabled in the current version. Until recently only Apple G4 systems had these extensions, but just as I was posting this review, Adobe publicly released an updated version which promised bug fixes and improved performance. I did see noticably better Lighting Effects filter performance as shown on the Application Tests page.