Ah- I mis-read that to mean 300' of baseboard.
To get ~28-30K out of it in 60' your talking ~450-500BTU/foot, which would usually require average water temps ~160F. The same 60' of baseboard should still be able to deliver ~10-12K at 120F water temps though, and if your heat load calc is correct that'll be close to the heat load for that zone roughly half the time, so you should still get a significant seasonal condensing benefit.
The cycling solution is to add thermal mass (buffer tank), then tweak the outdoor reset curves to where it's putting out ~150-160F water @ 0F outside. Then bump the curve temps down a bit if it's satisfies the thermostat in less than 30 minutes when it's 15-20F out. The burner shouldn't be cycling at all during thermostat calls at 25F or below if your heat loss calc & curve is correct. It might at warmer temps when the whole house load is below the min-modulated fire, but with even 10-15gallons of additional water to work with the burns should exceed 10minutes even when it's 50F out (very light loads.)
To get ~28-30K out of it in 60' your talking ~450-500BTU/foot, which would usually require average water temps ~160F. The same 60' of baseboard should still be able to deliver ~10-12K at 120F water temps though, and if your heat load calc is correct that'll be close to the heat load for that zone roughly half the time, so you should still get a significant seasonal condensing benefit.
The cycling solution is to add thermal mass (buffer tank), then tweak the outdoor reset curves to where it's putting out ~150-160F water @ 0F outside. Then bump the curve temps down a bit if it's satisfies the thermostat in less than 30 minutes when it's 15-20F out. The burner shouldn't be cycling at all during thermostat calls at 25F or below if your heat loss calc & curve is correct. It might at warmer temps when the whole house load is below the min-modulated fire, but with even 10-15gallons of additional water to work with the burns should exceed 10minutes even when it's 50F out (very light loads.)