If you drink a poison bottle as a Sin X, you can get a slight ASPD increase, I can't remember the formula offhand(I think it's a percentage). Depending on the server's rates, setup, customization, etc, this usually can end in a wasted effort.
I've had a lot of opinions on Sonic Blow Sin Xs, and I will pretty much just toss it out there. Sonic Blow takes no skill, requires buffs and a link, and most of the time, users of the build talk like they're gods. We had a kid on ArdentRO who just one-shotted everybody with an Infiltrator and thought he was top dog. Until he was divested and then looked like a fool.
SB is fast, one-shot damage that is usually fatal.
Crit is also fast(depending on your server) and the right equipment and a little forethought(such as carrying converter scrolls with you at all times) can usually rip an SB Sin X to shreds. Hell, I've killed SB kids while using a Dual CritSword build on FaithRO, some of their reactions border between priceless and absolutely insane(With my favourite being, "ill find ur house and kill u rl NOOB").
Out of curiosity, what server rates would we be talking here? LR, MR, HR?