To avoid duplication of efforts: I’m currently working on improving the existing support for the Insteon 2441TH, in particular cutting down the amount of polling, parsing out-of-band messages etc.
The improved thermostat support is ready. The pull request is: #3205
Somewhere in the pull request there is a link to a compiled jar file that you can drop into the addons folder. Works with OH 1.7 and 1.8