Text is ideal for instance rendering as you are likely only setting a the fontpage texture only once for a large amount of text and use atlas texturing and alpha blending to end up with the correct character on the on screen quad. Since you are using a quad the data that is in each vertex buffer for each character is very small, GPU's don't like small Vertex Buffers, so batching these up to a sensible maximum will increase throughput on the GPU and hence improve performance.