in anands article, he said that like on lynnfield, the odd multi can get you higher than the even one.
my 530 doesnt like anything north of 225 with 21x multi, and doesnt like it with 215 on the 22x.
above 215 on the 22x i lose usb devices from time to time, i think that if i had the 23x i could get 4.8 and approach 5.0 on air if i get lucky enough.
i think anand said that the even multipliers at high frequencies have interference troubles as far as clock generation goes. from what ive read elsewhere, they say that even multiplier would require higher vcore at the same frequency obtained using an odd multiplier. from my own experience, i think the former is more accurate as i usually get a fat no POST when trying to shoot for known good speeds and voltages when switching from 21 to 22 multiplier at lower BCLK speed.
i dont know why it would be more stressful to move to the higher multiplier; the QPI link speed is higher on the 21x multiplier on my board than the 22x would be.