I have a pair of AR-4x and love them. Unfortunately, they are relatively insensitive. I don't think they're above 87dB, maybe 85. Nevertheless, they drive well and sound great with my Scott amps (20-25WRMS per channel) and Fisher receivers and amps (25-35WRMS per channel). Your Eico is a great amp, but a little light on power, so, as KentTeffeteller says, you'd want something probably in the 90 dB range for your Eico.
Dave
PS Kent, I haven't found many (any?) acoustic suspension speakers that are much better than mid-80 dB sensitivity, although admittedly it's hard to find the actual specs for the AR-4x.