That depends on how you define "speed". In terms of measurable "speed", the O2 has sufficient high frequency extension, flat response (less than 0.1 dB variation from 20 Hz to 20 kHz and no significant phase shift), and slew rate (can output a nearly 48 kHz tone at full scale 20 Vp-p voltage) that it should not have problems with reasonably well reconstructed - that is, not with a NOS DAC or other device that outputs a lot of ultrasonic/RF garbage - CD quality digital audio. Whether it has enough PRaT or whatever in sighted subjective listening, it is mostly down to individual biases and other factors.
Ultimately, you either trust - even sub-consciously - the objective approach or you do not. In the latter case, just buy the most expensive amplifier you can afford, because you will never find peace of mind with the O2 or other low-ish cost amplifiers, and you will end up "upgrading" anyway, spending more than if you just skipped the alleged lo-fi gear in the first place. Otherwise, you may also consider the possibility that using different headphones, rather than amps, could give the best sound.
Edited by stv014 - 2/25/14 at 4:17am