I think SH and ICOM debate is that they are as good manufacturers as each other.
Looks like the SH GX1200E and GX1300E are available at the moment for £99. Or the Icom M323 or SH GX1700E for £159. I'd agree the M323 and 1300X seem very similar and while I follow your replace it 1/3rd often logic - if you had £159 burning a hole in your pocket the 1700 has a built in GPS, bigger screen, chunkier radio, supports the RAM mike (not cheap!) so that your radio could be better protected from the elements, IPX8 water proof rather than IPX7 of Icom. (of course that just means they test to a different standard the Icom may pass that standard too but not been tested.)
I think the other think in my mind would be what will you be interfacing too? Plotter? AIS? Would you want a position from the DSC to the plotter - best check thats possible with all the models, would you want to be able to call an AIS target from the plotter screen - again thats only possible on certain models...