I`ve seen normal, non-S barren get up to like 1350 (yesterday I got a 1343), but there are also S.class barrens that can get 1700 & maybe higher.
If you aim to keep barrens 1.2k+, you can consider your C2 VERY decent. & at that point, it`s more efficient to enlarge it afterwards with gordo`s then to keep spending turns trying to find larger ones, because those 1.3k+ are VERY rare.
E.3576 Barren 1,343