At anything near the price point of your GPO5 upgrade, nothing exists that would be a step up from what you already have. High-end orchestral libraries are expensive.
If you don't mind dongles (I do mind them), then the most cost efficient "full orchestra" solution that would be a step up would undoubtedly be from EastWest. Since I don't use their products, I'm not intimately familiar with them, but they have a range of orchestra lines, and very often have massive sales. They also offer a composer cloud service where you can access the libraries online for $30 per month or something, which might be an inexpensive way to try the libraries and see how you jibe with them.
Or you could explore some of the lighter "ensemble-based" libraries to augment GPO. CineSymphony Lite from CineSamples is 25% off right now still I think, and the new Orchestral Tools Berlin Orchestra Inspire looks like a steal for the intro price of β¬249... OT makes top-shelf stuff, and I'm pining for this library myself...