help with s/n ratios of preamps and Moving Coil

thanks. the gain on the clearaudio smart phono that i ordered is 54db for MC, and my cartridge is rated at .5mv at 3/5 cm/s. So >68db will be fine ? Its just strange that there are cheaper phono stages than the clearaudio that have a higher s/n ratio >80db for MC. but their THD and channel separation values are not as good as the clearaudio. For example the Cambridge 640p. What gives?

Yes, everything will be plugged in via a AC line filter. I am used to a much cheaper NAD pp2 pre-amp with this cartridge and have no idea what the s/n ratio is but it sounded good to me.

I can only hope the that clearaudio smart phono will be a noticeable improvement. Audio guys at the store said to completely ignore the numbers and concentrate on the overall quality of the preamp and that clearaudio makes really good stuff. I guess, if it doesnt work ill just have to switch to a MM cart, the S/N spec for which is higher on this preamp. Sorry im very new to vinyl, and not having the new preamp for another week or so is making me ponder all this stuff.

oh and btw.. does the S/n ratio include the noise level of the pre-amp itself. for example, some cheaper preamps may create their own noise levels and their s/n ratio's maybe higher taking that into account; while a more expensive preamp may be dead quiet itself and has a slightly lower S/N ratio. Does this make sense ?

I guess the other thing to consider is @ what frequency manufacturers rate the S/N ratio for MC carts. Ive seen some examples rated at 20kHz and some at 1kHz.