About Clear Register...

CPU	mov eax, 0	xor eax, eax	sub eax,eax
Pentium	1.0/1.0	1.0/0.5	1.0/0.5
Pentium with MMX	1.0/0.5	1.0/0.5	1.0/0.5
Pentium Pro	0.5/0.5	1.0/0.5	1.0/0.5
Pentium 4	0.7/0.7	0.5/0.5	0.3/0.3
Prescott	0.4/0.4	0.5/0.5	0.3/0.3
Core Duo	0.5/0.5	0.5/0.5	0.5/0.5
Core 2 Duo	0.3/0.3	0.3/0.3	0.3/0.3
AMD K5	0.5/0.5	1.0/1.0	1.0/1.0
AMD K6	0.5/0.5	0.5/0.5	0.5/0.5
AMD Athlon	0.4/0.4	0.4/0.4	0.4/0.4
AMD Athlon 64	0.3/0.3	0.3/0.3	0.3/0.3
VIA Nano	1.0/1.0	0.5/0.5	1.0/1.0

Source : http://instlatx64.freeweb.hu/