You've to personally inspect the chip.
This list i have is getting outdated.
CPU (Duron 600) Overclockability
AKAA0022MPMW Week 22 800 - 850Mhz at 1.8v
AKAA0022MPMW Week 22 800 at 1.55v
AKAA0024DPBW Week 24 800 - 850Mhz at 1.85v
AKAA0027BPAW Week 27 900 - 950Mhz at 1.85v
AKBA0029TPAW Week 29 900 - 1.0Ghz at 1.85v
AKBA0029FPBW Week 29 1Ghz: 1.75V, 1.02Ghz at 1.825V 1.03Ghz at 1.85V
AKBA0031WPEW Week 31 1030Mhz at 1.8v
AKBA0031UPHW Week 31 1Ghz at 1.725
AKBA0031GPAW Week 31 900 MHz at 1.55Vto 1000 MHz, 1 GHz at 1.75 V.
AKBA0032EPAW Week 32 900Mhz at 1.8v
AKBA0033FPJW Week 33 900Mhz at 1.8v
AKBA0036APAW Week 36 1.0 - 1.05Ghz at 1.75v
AKBA0036APBW Week 36 950Mhz - 1Ghz at 1.80v
Duron 650
AKBA0038DPGW Week 38 1.0 Ghz at 1.7v
AKAA0023SPAW Week 23 850Mhz at 1.75v
Duron 700
AKBA0030XPBW Week 30 860Mhz at 1.75v
AKBA0030WPCW Week 30 900Mhz @ 1.55V, 1Ghz @ 1.75V and 1070Mhz at 1.85V
AKBA 0035DPBW Week 35 900Mhz at 1.60v, 1Ghz at 1.85v
AKBA0038EPIW Week 38 1.0Ghz at 1.75v
AKBA0040SPDW Week 40 900MHz 1.65V, 990Mhz at 1.80v