VARIANT_OVERLAP_GROUP_THRESHOLD parameter exploration (My MacBook Pro)
0. VARIANT_OVERLAP_GROUP_THRESHOLD = 1, 240.28s, 327MB
1. VARIANT_OVERLAP_GROUP_THRESHOLD = 5, 239.66s, 334MB **BEST**
2. VARIANT_OVERLAP_GROUP_THRESHOLD = 6, 241.10s, 334MB
3. VARIANT_OVERLAP_GROUP_THRESHOLD = 12, 247.32s, 354MB
4. VARIANT_OVERLAP_GROUP_THRESHOLD = 5000, (unique group for every key), 264.54s
5. VARIANT_OVERLAP_GROUP_THRESHOLD = 0, (all record keys mingled) 222.40s, 297MB