Should I use -march=nocona or -march=core2 when compiling binaries for this processor with gcc 4.3?

vendor_id       : GenuineIntel
cpu family      : 6
model           : 15
model name      : Intel(R) Xeon(R) CPU           X3220  @ 2.40GHz
stepping        : 8
cpuid level     : 10
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni ssse3 cx16 lahf_lm

I cannot really find if this CPU is already core2 architecture... Only find information about the quad core variants, but this CPU is only dual core.