Grammatophyllum speciousum growth rate?

[Laserbeak]

I got what I now believe to be a Grammatophyllum scriptum for free from my neighbor, but while researching it, I became fascinated by the Grammatophyllum speciosum, the world's largest orchid.

I ordered a specimen that's supposed to be well established in a 4" pot. How fast do these things grow? I do have a couple big baskets but not much in between.

Any tips would be appreciated. Thanks!