The composition on both looks great but I think the conversion is a little off…just an opinion. They seem harsh and the second one you loose the detail in the tree in front of the tower – so much so that the parts you do see are a distraction. The sky is also blinding out the detail of all else.
If you try these again but reduce the contrast? I find that with post processing the mantra is to increase contrast and make sharp. I also found that reducing contrast makes for a better B&W with smooth finishes. Try to take the edge off the sky in the second one – either burn in the mid tones or if using CS3 have a go at reducing the cyan and magenta.
And a suggestion would be to apply a gradient adjustment layer from black to white and set the blend mode to soft light to darken the top level of the sky. It helps to contain the focus within the image, not let fly up into the white space.
Keep them coming though.
I would prefer the first one myself. But they do seem too dark and contrasty.
You did a better job capturing Glendalough than I did though, well done :P