Well, it is what I thought:

const int VectorBoolOrBitsetTestBitSetVectorized(Bits& buffer, const Vector<unsigned char>& randVec)
{
	const int count = randVec.GetCount();
	for (int i = 0; i < count; i += 16)
	{
		// Use the vectorized set method.
		buffer.VectorSet(i, &randVec[i]);
	}
	int alloc = 0;
	buffer.Raw(alloc);
	return alloc;
}

This is not the proper benchmark. The large part of work is already done by grouping input bits into randVec, which is not included in the benchmark time IMO.

If you wanted the proper benchmark, you could e.g. set randVec to random values and then set bits in Bits for those values that satisfy some condition - that IMO will benchmark scenario closer to the real use. E.g. (for original Bits and random 0..100):

for(int i = 0; i < randValue.GetCount(); i++)
    bits.Set(i, randValue[i] > 50);

buffer.Set(i, rand[i]);

// vs.

buffer.VectorSet(i, &randVec[i]);