Will these arms hold a 34-inch ultrawide or a heavy OLED?

It depends on weight, not just size. Community reviewers report standard 19.8 lb arms sagging with some 34-inch ultrawides even when nominally under the limit, while heavy-duty models like the HUANUO TitanLift (rated to 44 lbs) are described as 'solid as a rock' with a 34-inch OLED. For large curved or OLED panels, buyers we read consistently recommend a dedicated heavy-duty arm over a general-purpose one.