I agree with Angry Sci - get the full SR group, and replace the cassette in 20k miles. Or, get the whole group, and SELL the expensive SR cassette, and buy 2 Chorus cassettes!
Either way, no matter how much value you lose by getting SR, nobody will ever stop you and say "you should have got Chorus on that bike"!
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'11 Time NXR Instinct / '79 Paris Sport by Moulton