How to sample 5000 variables with EmbeddingComposite.sample_qubo()?

https://github.com/dwavesystems/dwave-system/blob/32e9065cddeb123106b43d947877043c1a2ccc78/dwave/system/composites/embedding.py#L47

This code produces a correct solution. It is basically a very simple **Max-Cut Problem** of 256 vertices with a known solution.

```
num_vars = 256

graph_list = list()
for i in range(num_vars-1):
graph_list.append((i, i+1))

G = networkx.Graph()
G.add_edges_from(graph_list)

Q = defaultdict(int)
for i, j in G.edges:
Q[(i,i)]+= -1
Q[(j,j)]+= -1
Q[(i,j)]+= 2

sampler = EmbeddingComposite(DWaveSampler() )
response = sampler.sample_qubo(Q, chain_strength=4, num_reads=10000)
```

Unfortunately, however, as soon as more vertices, say, `num_vars = 1024`, are used, the program will never produce the theoretically correct result, which is supposed to have `num_vars - 1` cut edges, and `num_vars/2` vertices in each set.

Could you please help me reach the goal of as many vertices as possible, say, 5000? After all, it is claimed that D-Wave hardware is capable of handling more than 5000 variables.

Thanks.