Which method is better? [ Memory-wise ]

Okay so I am about to make a large semi-circle boundary in which objects can't enter.

My game is already too heavy (lots of sprites, particles and events), so I was wondering which of these will consume lesser CPU/GPU usage:

1. Having a semi-circle sprite (1600x800 px) with around 25 point collision polygon
--OR--
2. Use Compass-Arc method and only draw a dotted-boundary using 50 small sprites ?

(Meaning, using one thin radius-long sprite as a temporary guide, rotate around the Origin, while spawning total 50 small dots [10x10px] equally along its edge using Repeat and Rotate event-action)

I hope it makes sense? Simpler question is: 1 Large Sprite vs. N Small Objects

Thank you