Any performance concerns with sending a buffer array in express JSON response?

My nodejs server consumes data from a nodejs JSON API. Some endpoints on the API return image data like so:

let buffer = await getImageBuffer();
res.set('content-type', 'image/png');
res.end(buffer);

Which works great. However for a number of complexity reasons, I'd love include a buffer array in a JSON response instead... like so:

let buffer = await getBuffer();
res.json({
  contentType: 'image/png',
  buffer
});

Are there any performance issues w/ including a buffer array in a JSON response like that? Is there any inherent performance benefit to using res.end(buffer) instead? The consuming server is also running nodejs, and will naturally JSON.parse() the response from the API.