the latency is also determined by which server you play on, they all have different locations and different routing applied, for example on my main server Ravenholdt i get around 300-350ms, on my friends server bronze dragonflight, i never go above 270 ever. And that is running unshaped webafrica, no registry hacks nothing, plain line (4mbit). Personally i dont believe just having 384 is decent, because the second your line starts using team speak or vent, that 38KB/s is not adequate. I use team speak and my lag still doesnt even move, thou my friend with 384 when he uses it, he starts to get a bit of latency. But its all down to personal expierence i guess, some people it happens to , some it doesnt.
My advice would also be to go to a few servers to roll some low toons to see what the server is like before you play there for good. another example, spinebreaker is laggy as hell, i would get like 500-600ms there with unshaped. Terrible latency.
Bronze dragonflight is well populated but the maturity level on that server is something to be desired.
Ravenholdt has been around for many years, i have been on there since oct 2006, and will never budge, the raiding is top notch on that server. its a RPPVP server, so you can pvp and RP and PVE. The que waits for PVP are minimal , longest ive ever waited was a bout 4mins.