Hi, hamed-khorrami. Bigger is better from a flight stability standpoint. A 10% increase to the plan size should be a pretty easy enlargement, just be sure to bump yourself up an engine size to compensate for the extra size and weight.

Making the wing with zero dihedral will help the plane perform axial rolls and inverted flight a little better. It could change some of the the gentler flight characteristics a bit, though, as well. Just make sure you're looking for an aggressive sport plane instead of of a well-rounded sport plane before you build the wing without dihedral.