I only have rounds, but my mom has heart-shaped diamond studs. Hers are 1.5 cttw. They are pretty when they are straight, but it drives me crazy when they spin.
As for the evening parties question, I do not know if there is an answer to this. IMHO, as long as the stones are cut well, have great color, and have only small inclusions, then size does not matter. To me, sparkle matters the most!