I like ~4 inch flippers too. A few months ago I went to Ace Of Knives and handled a number of different models, including small and large Sebenzas, but nothing came close to the feel of the Olamic Wayfarer in carbon fiber (4.25 inch CPM-154 blade). After waiting a few weeks to make sure it wasn't just a passing interest, I bought one. It's a little spendy, but I'll enjoy owning it for the rest of my life. I highly recommend that you try to handle as many folders as you can before plunking down your cash. Make sure you can easily return something you just don't like. Buy from stores with a good return policy. I was surprised that I didn't much like the feel of Hinderer and most of the cheaper ZT stuff. The CF Wayfarer felt like it was molded to fit me.
A couple days ago I received a used SpyderCo Southard which I bought through Blade Forums for under $200 - it is a very nice 4 inch flipper. At first it was too stiff, so I applied a little Break Free CLP on the bearing, which smoothed out the action quite nicely. The blade is CTS204P, which is similar to M390. You'll need a diamond or hard ceramic sharpener for this blade. The blade is very stout, and has zero play.