I think that if you are in a well covered area you are unlikely to see any drop in performance with the '4' by holding it wrong. But if you're in a marginal signal area the attenuation caused by your hand has the potential to be significant. The funny thing is that Apple's OS update to correct the # of bars displayed may actually make the signal attenuation more noticeable (in the graphical sense). Right now, given the 50dB spread that Apple's 5th bar represents and anandtech's measured ~25dB drop with the wrong grip as long as you have less than 25dB signal loss you will never see the additional signal attenuation reflected on the phone's graph. If you had a numeric reading of signal strength instead bars you'd probably see something, although it's probably the case that you're simply well-enough covered in NYC to have it not matter.