At that scale, the larger plane will make not one iota of a difference!

5-10 feet further out the larger plane will look exactly the same as the smaller one.... and 10' is not a big distance.

Get either, although the .40 size is really fine, and learn to fly them closer in to you if you are having difficulting seeing them.

Also put loudly colored strips of different colors on the wings and tail to help you maintain orientation.

Work on being able to tell the orientation of the plane by how it flies, and not by actually seeing it. In other words, if the plane is a dot in the sky, you should still be able to tell which way it's pointed and going by the way it responds to your inputs.

Simulators are fantastic for this, particularly the more advanced ones. By turning on smoke trails in the sim you get an aid that helps you obtain your bearings as you practice shoving the "dot in the sky" around.