It's absolutely a speed optimization, although more for reads than writes. The 64-byte cache line bit is a standard blocked Bloom filter. Add SIMD queries and that's about as fast as these things get.
The other side of the tradeoff is bumped ribbon retrieval. Blocked Bloom filters are about 50% bigger than BuRR.
The other side of the tradeoff is bumped ribbon retrieval. Blocked Bloom filters are about 50% bigger than BuRR.