I took the 70-551 Upgrade exam to upgrade my MCAD to MCPD (Web). Ultimately, I would like to get the MCPD 3.5 Enterprise after getting the MCPD 2.0 Enterprise and would like to do it with the minimum number of tests.
What exams should I consider taking next?
Once you get your MCPD 2.0 Enterprise certification, the shortest path to MCPD 3.5 Enterprise will be the upgrade exams:
Exam # 568 - Upgrade Part 1 Exam # 569 - Upgrade Part 2
To check other paths, I would recommend you log into the MCP member site. From there, on the left side menu, you can open [View My]-->[Certification Planner]. Then, pick any certification (e.g. "MCPD - Enterprise Application Developer 3.5") and it will show you all possible options based on your current transcript.
Good luck!