A bit of bad news: ISR G1's max out at 15.1M (your 878, 1841, 2801).
For the other software recommendations, at this point I would use one of the Cisco Suggested releases as long as they are MD and have a few revisions under their belt (e.g., 15.4(3)M6a MD).
With the frequency security vulnerabilities and patches are released, you'll be in a constant upgrade and/or workaround cycle anyway.