MS290 was a top seller when I sold Stihl out of a dealership. We sold 99.9% of them with 20" Bars and .325 Full Comp Green-Label Chain. Yeah, usually 26RM2-81 which I think is a bit conservative for any saw user, even newbies. If my customer was somewhat experienced I would suggest buying yellow label chains for "spares". The dealership I worked for sold saws with pretty much the longest recomended bar on them. MS290's, 260's, and 270's all got sold with 20" bars not because it was the optimal bar for the saw, but because it was what the customer wanted. And to be honest, most of the staff, including management, didn't know any better. If I had it my way, I would have taken those 3 saws built on that chassis, the 290, 310, and 390; and set them up with 16", 18" and 20" bars respectively.
The MS290 is certainly capable of running a 20" bar but if you're looking to keep up with your buddy's MS361 you're gonna be disappointed.