Why are you and others so against encoders?
Because your machine should be 100% reliable if set up correctly. Adding encoders won't make it any more reliable, they'll just give you the opportunity to stop it when things go wrong.
If you have a NEMA 34 or larger motor you have literally 5 times the torque I do. 380 oz-in motors don't have much overhead when driving against a 1/2" bit mounted in a router plowing through hardwood plywood. Feed rate changes as little as a few IPS under those conditions make the difference between a toasted bit and a successfully cut part.
The issue here is that you have a machine capable of a certain level of performance. You want it to perform like a machine with much higher capabilities. Encoders aren't going to do that. The "overhead" that you mention is up to you. The reality is that if the machine stalls or loses steps, then you should be running at least 15%-20% slower than you're trying to. That's how you get a reliable machine.
As far as burning bits. Try slowing down the rpm. As far as achieving recommended chip loads. You'll need at least a 5-7HP spindle to achieve those, as 3/8 spiral router bits are easily capable of cutting 3/4" deep in one pass at 800-1000ipm. With a normal router for a spindle, you'll stall it instantly at those feedrates. When you have an underpowered machine (which most of us have), you run at reduced depth of cut and lower rpms to keep the bits from burning, while getting the most you can from your machine and it's capabilities.