Best very high cap glock mags for carbine use?

[Arizona_Mike]

Have early gen 2 glock 20 and a late gen 3 21. Also have carbine uppers for both 45 and 10mm I use with the 20.

I have some +5/+4 floorplates that make my 20 mags 15+5=20 and my 21 mags 13+4=17.
Want more/longer.

Mike