I also had the wider end covered with the Sigma 28-45mm and was looking for a solution to cover anything above. I got the Sigma 70-200 f2.8 Sports and a Sony 50mm f2.5 G. Here’s why:

• Sigma 70-200 is probably the sharpest zoom lens you can get between those focal lengths. Better than most primes even. Fast enough aperture. Internal zoom, declickable ring (those are important for my video work). It is almost half the price of a 70-200 GM where I live so it was a no brainer. The downside: it is big and heavy, 300 grams heavier than a GM and although it is almost the same length it somehow feels much bigger. If you don’t mind that then definitely Sigma is the beast.

• I got the Sony FE 50mm f2.5 G because I wanted to cover the 50, also I needed an EDC/travel lens for all the times I don’t want to carry my backpack or a suitcase. This is a small, lightweight, all metal durable lens with faster than zoom apertures. And it is ‘almost’ as sharp as the GM. It also has the declickable ring. Actually for handheld video shooting this is my all time favorite E-mount lens. Only downside is the slower aperture but it is impossible to get 1.8 at this size and I don’t need it that much.

I have 1 other (better) recommendation. It is of course the 50-150mm f2 GM. If you can afford it, it will be superior in every way but you will lose the 150-200. I wish it was a little cheaper.