You don't need a sample rate as high as 100kHz.

OK, so A4 is 440Hz. You could sample that at 112,640Hz to get 256 samples per oscillator cycle, sure.

But you could instead record an A1 (which plays at 55Hz) at 14,080Hz to achieve the exact same result. This is one reason why most samplers let you specify what the original note of the sample is.

With a piano or violin, playing an A1 sample fast enough to get an A4 note will sound atrocious, but with a static waveform, it will sound the same at any note.

Bear in mind CD players are only 44.1kHz, and they sound just fine. :)

As far as being one or two samples out goes, in my experience it doesn't make that much difference. If a sample loops badly, going from a very low point straight to a very high one or vice versa, it will make a click sound, and if it's only a single cycle, then the click will become an integral part of the overall sound. That and a shape that's cropped or has space after it during each cycle will sound different, but it would need to be more than a few samples out to be really noticeable, I believe.

Hmm, thinking about it, it would be possible to write some software that reads in a waveform, finds the first 256 zero-crossings, and stretches or squishes each resulting cycle into 256 bytes each, which would completely automate the process of wavetable-ising a waveform for you, without you having to worry about the original pitch or sample rate (other than for improving the quality). Tempting...