Focusing on large companies, fewer in number

I sell a solutions-based product to the banking industry. I sold this to mid-sized banks nationwide for several years, but last year decided to move to a larger company that focused exclusively on top-tier banks. With the mid-sized banks, there were about 800 potential prospects that fit our desired size profile. I could always put my head down and line up more meetings when I needed to fill out the pipeline. Here, I am only focused on about 30 to 50 large companies, and the rest are really too small to fit our model.

Any suggestions on making this type of transition, how to go “deeper” with accounts when you’re still in a cold calling situation, etc.? I guess what I’m asking is, after a year I have pretty well plowed through those 50 target companies and have gotten an idea of who is interested our help and who doesn’t. There isn’t an endless supply of new prospects so… how do I still maximize my prospecting time with a much smaller pool of prospects?