OK so results doing OC the manual way via wusy's C2D OC sticky (not good read to end).
Hardware: Retail C2D E4300, Arctic Cooling Freezer 7 Pro, Gigabytpe GA-965P-DS3 ver2 F10, Two 1 GB sticks Super Talent DDR2 667MHz CL5 Rigid with heat spreaders, older ATI 800 VGA Card, Seagate 7200.10 SATA2, Case=Ultra Wizard, Fans=Rear exhaust Apevia 120mm & front Apevia 80mm
Hardware Settings: Case=Closed, Rear Fan=On, Front Fan=Off
Global BIOS Settings Advanced: Limit CPUID Max. to 3=Disabled, No-Execute Memory Protection=Disabled, CPU Enhanced Halt (CIE)=Disabled, EIST=Disabled, CPU Warning Temp=60C
Global BIOS Settings MIT: Robust Graphics Booster=Turbo, Multiplyer=9, PCI Express Frequency=Auto (100MHz), C.I.A.2=Disabled, System Memory Multiplier=2, System Voltage Control=Manual
Software: OS=Windows XP, Intel TAT, CoreTemp=Beta 0.94, Gigabyte Easytune5=Latest version from GB & Easytune Center (For CPU Fan Speed), SpeedFan=4.32 Beta 17
Goals: Max OC with Tjunction0/1(Max TAT load) < 70C, Tcase(Max TAT load) < 55C
Test 1 Settings: CPU=1809 MHz, Workload=TAT Idle (Base Case)
Test 1 Results: Status=Stable, Vcore=1.30v, Tjunction0/1(TAT)=36/39C, Tjunction0/1(CoreTemp)=21+15/23+15=36/38C, Tcase=23, Fan=430RPM, Tsystem=32C, Tambient=24C
Test 2 Settings: CPU=1809 MHz, Workload=TAT 100%
Test 2 Results: Status=Stable, Vcore=1.264v, Tjunction0/1(TAT)=56/58C, Tjunction0/1(CoreTemp)=40+15/42+15=55/57C, Tcase=43, Fan=980RPM, Tsystem=32C, Tambient=24C
Test 3 Settings: CPU=2025 MHz (12.5% OC), Workload=TAT 100%, Time=1230PM
Test 3 Results: Status=Stable, Vcore=1.264v, Tjunction0/1(TAT)=57/59C, Tjunction0/1(CoreTemp)=40+15/42+15=55/57C, Tcase=46, Fan=1150RPM, Tsystem=32C, Tambient=24C
Test 4 Settings: CPU=2160MHz (20% OC), Workload=TAT 100%, Time=1235PM
Test 4 Results: Status=Stable, Vcore=1.28v, Tjunction0/1(TAT)=58/60C, Tjunction0/1(CoreTemp)=40+15/42+15=55/57C, Tcase=47, Fan=1300RPM, Tsystem=32C, Tambient=24C
Test 5 Settings: CPU=2250MHz (25% OC), Workload=TAT 100%, Time=1240PM
Test 5 Results: Status=System locked up, rebooted, no monitor signal POST screen etc, rebooted, noticed no harddisk light activity
1250PM Took side door off PC, nothing smelt burned, when try to boot, PSU comes on, rear case fan comes on, after few seconds CPU fan comes on, no harddisk activity, no monitor activity POST screen etc.
100PM Removed 2 RAM sticks, booted, beep as expected, re-installed 1 RAM stick, machine booted OK (big sigh of relief), shut down PC
1:05PM, Re-installed second RAM stick, boots OK.
Decide no more OC "fun", waiting on advice please . . .