Hi Dave,
I'm in the middle of replacing my 4500 with a 5500.
I chose the 5500 over the 5400 for one primary reason:
- I wanted a unit that shared the same bottonology, and associated source code, as the other models (5600, 5700, 5800).
The existing 4500 hole is to narrow horizontally and to tall vertically. To get around this, I designed a bezel to sandwich between the panel and 5500. I've a mock version cut out of clear acrylic on a laser cutter. The final version will be black acrylic and should match the 5500's bezel and dark grey panel very nicely. Let me know if you'd like the DXF CAD file.
There are some changes in the wiring. Fortunately, I did my wiring in CAD so I'm in the process of updating the drawings and noting the differences. I expect to end up with a "punch list" with simple move pin X to position Y.
Good luck,