I would say a 300w like the hadco would be good for many LED jobs. you still have voltage drop when 200 feet away from a trans with a 20 watt load. also folks doing more LED are using 18 and 16g, thinner wire to take advantage of the lower price and lower load and just using higher taps. 18g spt2 is rated for 10 amps, or 120 watts, but probably only for 75-100 feet or so. if you keep your runs under 50 watts, which in LED would usually be 6-8 fixtures, you can probably use 18g wire and the 15v tap and easily be within LED spec.
not really sure if you realize much cost savings going from a hadco 300 watt to a 100 watt. most of what you are paying for is the timer and or photocell, stainless case, taps, cords, circuit breaker, plug in timer area, etc. I can't imagine a 100 watt being much cheaper.