I was interested in the low end of velocity/energy for 177 that will take out the rams. I didn't know if it was possible or practice for a airsmith to tune the Daisy 853 for sufficient velocity/energy to do the job. Or is that like trying to turn a VW into a Proche!

Most FWB300's are tuned around 600+. I would think in calm wind you could get away with 550+. It's not so much knocking them down I believe as much as the dwell time at that velocity is
so long that wind becomes a HUGE factor. The animal itself will fall fairly easily...

Rather than worry about velocity, focus more on the pellet choice. SB Silh doesn't focus on velocity, nor should you with an airgun. One choice that comes to mind is the JSB Express, a 7.9gr pellet. For your combo, it would give a slightly higher (25+fps) velocity, however, better aerodynamics. Another good one is the Crosman Premier 7.9gr (in the cardboard box).

10M match-style AR have a loopy trajectory, however, if you have the pellet drop determined you can shoot well.

For the cost of increasing velocity (if it can be done to a consistent level) will be higher than purchasing a new AR.

In AR Silh the distances are fixed, once you have your scope marked I would just recommend practice, and practice.