stock maybe 23 but that doesn't mean it's the best setting to use for overclocking the i7 with DDR3 1600. We want to maximize our performance and this is best done by keeping our sub-systems performance levels in sync. A BCLK of 200 is the magic number but keeping the BCLK in the 195-205 range will offer you your best performance curve.
19 x 195 = 3.7GHz, with a memory ratio of 8 our memory runs at 1560MHz
19 x 200 = 3.8GHz, with a memory ratio of 8 our memory runs at 1600MHz
19 x 205 = 3.9GHz, with a memory ratio of 8 our memory runs at 1640MHz
20 x 195 = 3.9GHz, with a memory ratio of 8 our memory runs at 1560MHz
20 x 200 = 4GHz, with a memory ratio of 8 our memory runs at 1600MHz
20 x 205 = 4.1GHz, with a memory ratio of 8 our memory runs at 1640MHz
21 x 195 = 4.1GHz, with a memory ratio of 8 our memory runs at 1560MHz
21 x 200 = 4.2GHz, with a memory ratio of 8 our memory runs at 1600MHz
21 x 205 = 4.3GHz, with a memory ratio of 8 our memory runs at 1640MHz
22 x 195 = 4.3GHz, with a memory ratio of 8 our memory runs at 1560MHz
22 x 200 = 4.4GHz, with a memory ratio of 8 our memory runs at 1600MHz
22 x 205 = 4.5GHz, with a memory ratio of 8 our memory runs at 1640MHz
etc....
If you try to use a 21 multiplier 4GHz is harder to achieve.
21 x 190 = 3.99GHz and you can run the memory at 1520MHz or 1900MHz. 1520 is slowing the performance while 1900 is going to overload the system.
If you try to use 22 for 4GHz then you windup with
22 x 182 = 4.004GHz and your memory winds up at 1456MHz or 1820MHz
etc...
This trend continues until you hit a 25 multiplier at which time you can drop the BCLK to 160 for
25 x 160 = 4GHz and with a memory multiplier of 10 we get 1600MHz.