Question Overclock Cpu in GA-M61PM-S2

Aug 6, 2019
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i am using :
  1. amd athlon ii x4 620 , 1.6Ghz
  2. PSU 500 watt
  3. 6gb Ram ddr2 400Mhz
  4. Vga gtx 650 ti

i want oveclock my PC, but i have overclock just 2.8 Ghz using overclok in bios, with FSB 215, Multipler x13, HT speed x5, NB x10
why i am increase FSB more than 215 its will be downgrade processor speed, ?
exp , fsb 300, and multipler x13 i get 1.4 Ghz ,
sorry for my bad english