Yes there are numerous differences that one can face, the major points are the speed and cas latency of the ram, getting something different from what you have will at best cause it to run at the slowest speed, therefore penalising your speed, other issues may involve a finicky motherboard only accepting certain combinations of ram (max sizes etc).
I would strongly suggest sticking with the exact same ram to minimise possible problems, getting another brand or even more so a no name brand you have no idea if it will work or not.
One thing I will ask though, are you intending to get this new stick to enable hyperthreading ?
Because if you are you may be better off selling that stick you have and buying a matched pair of ram, at least that way you are guaranteed that they will do the job you got them for, just a thought.
I would strongly suggest sticking with the exact same ram to minimise possible problems, getting another brand or even more so a no name brand you have no idea if it will work or not.
One thing I will ask though, are you intending to get this new stick to enable hyperthreading ?
Because if you are you may be better off selling that stick you have and buying a matched pair of ram, at least that way you are guaranteed that they will do the job you got them for, just a thought.