Copper coils are the best but were out of my budget. Did quite a bit of research on the web and decided that PEC is second best choice. The "experts" claim it has better flexibility for the expansion/contraction of the concrete than the copper, but the copper does have the best heat conductivity. You are going to have zones, whether you want them or not because you want to return the water to the boiler/heat exchanger with some heat still in it. The TEMP Delta does not need to be too wide, or it takes too many BTUs to get it reheated for circulation. In the larger section of my shop, I have three closed loops feeding from one manifold and the smaller section has the same. One thermostat in each section controls the pumps and these thermostats are located about the center of an interior wall. The pumps are 24 volt DC TACOs that have been used in industries for a long time and have a good track record.
Convection heat rises and it is very warm next to the ceiling when it is used. This is really wasted heat unless you want to install a system to return it into the ducts. Radiant heat does have some raising but tends to warm objects. The warm floor means warm feet and very comfortable on a creeper so the thermostat can stay low and still be comfortable. My office/bathroom is located 11 ft up and is not heated. It is about 7-8* cooler than the floor level. We have a small electric heater if we are going to be in the office any length of time and because the office is also insulated inside the insulated shop, it warms up quite rapidly. Of course, you don't linger on the throne if you had not planned your daily constitutional. This spring, we will install a Mitsubishi ductless heat pump in it that will cover our needs