t1mmbo,
3/8 dia tubing is pretty small. You will have a decent amount of friction loss in PSI and from what I can tell from this winters posts, a reasonable chance of ice blockage. I would use at least 3/4" if you're going 250'. Rather than using tubing it may be less expensive if you use 3/4" or larger PVC from the compressor to the pond edge and then adapt the stubs to receive the EPDM tubing from the compressor and the feeder tubing to go to the diffuser.
CB, Soaker hose (although not the most efficient way to aerate) works the same way that membrane diffusers or airstones work. Aeration via diffused air occurs from the point of bubble rise upward. So, hypolimnetic aeration is not so much a function of the type of diffuser as the placement of the diffuser in the water column.
