I don't think you can achieve any improvement by going over 24-bit/44.1 kHz or 48 kHz when recording from an analog vinyl source. You can't achieve a better s/n than 16-bit can reproduce (= 96 dB). 24-bit can be useful if the recording volume is set to a lower "safe" level and if you do some processing with an audio editor. As far as I know, 96 kHz does not provide any audible advantage.
Even many professional recording engineers are not certain if 96 KHz provides any advantage over 48 kHz when working with original digital masters. Sometimes 96 kHz is used only because the label is going to publish a DVD-Audio or SACD version of the recording and the marketing promises of "high" resolution audio must be met.
In any case, have you tried wave playback for testing the resampler's CPU usage separately? I'd guess that the most of the CPU is needed for resampling, not for decoding. MC has a high quality Shibatch resampler that uses a lot of CPU.
With lesser HW you could try 48 kHz. Conversion from 96 kHz to 48 kHz is less complex than to 44.1 kHz. This would also avoid an extra resampling step because most cheap soundcards can't handle 44.1 kHz. A 44.1 kHz signal would be resampled to 48 kHz anyway before doing the DA conversion or sending the output to SPDIF.
