I am wondering the same thing. I bought a 10 1/2" diameter light to go over my small island, but I don't care for the looks of a small single pendant. I purposely only bought one even though I need something for over my sink as well. When my first one comes in I will decide if I should put it over the island, the sink, or if it is too big maybe use it to replace my foyer light.

My island is 4' x 4.5' . I also wanted those pendants but my island is too small for them. I ended up choosing the George pendant from Rejuvenation.

Here is a link that might be useful: George pendant

I have two 8" pendant lights over my new peninsula that is about the same size as your bar. I do have a cabinet at the end of the peninsula, but the pendants look just fine, and not too big. I basically have 12", pendant (8), 12", pendant, 12" cabinet. (measuring from end of peninsula back toward wall). It looks good.

My GC said they were too big, but DH put one up and then we measured (our issue was the one had to be far enough away from cabinet so door wouldn't hit it). I loved my lights so we went for it. I am happy.

Have you done the balloon on a string mock-up? That will help you visualize the spacing and size.

I was going to suggest the George pendant also. They're about 5" wide, customizable for metal and shade color, and are very cute IRL.

So would a 10" pendant over a 36" sink be too big?