One way to look at this is what one has on-hand, if anything. For example, I came to pattern from electric sport flying. I already had 6S set-ups, so my Osiris got the A50-16S at the time. That was a few years ago. If I were to start-over, I would go 5S: A little lighter and the 5S packs can be paired in series to make 10S for a 2m set-up. There are other ways to look at this, no doubt. Weight, flexibility for other uses of the LiPos, etc. and some matters of preference. Why not give 5S a try since you are going for a pattern set-up?

Good choice giving the Monolog another look: Arch is right, there are some really good deals and BJ Craft is producing excellent value products for the various price points.