A Caulker Cay will generally be within the 4-6 feet range that you are looking for. The Longicaudas, depending on gender, will generally fall in the 6-9 feet range. Personally, I like the coloring of the Loncaudas over the Caulkers. I have worked with both in the past, and didn't have any notable, consistent, issues with temperment. Good luck making your decision.