If I want to record (to .WAV) at 24 bit precision, 48 kHz, (instead of the default 16 bit/44.1 kHz) will a typical home-use SATA II (3 GB/sec) HDD, running at 5400 rpm, with a transfer rate of between, say, 100 and 140 MBs, with an entry level cache of, say, 64 MB, have sufficient performance to satisfy Vinyl Studio's buffering needs? Or should I consider SATA III (6 GB/sec) to be the minimum requirement?
No, that will be fine. Recording with those setting will be using only a tiny fraction of the disk's transfer rate.