In relation to energy efficiency a triple glazed unit has only a slight benefit compared to an "A" rated double glazed unit. A triple glazed unit is double to cost of a double glazed unit as the 3 panes have to be toughened. Triple glazing is only advantageous for noise.
Bear in mind the difference in climate to Ireland from where you are buying your joinery. Sweden/Scandanavia/Poland have a crisp dry cold atmospehere whereas Ireland has a wet damp cold atmosphere therefore the lifespan/preformance of the joinery would be totally different in the two countries. Hardwood (Iroko) is the most suited to Ireland.
Also think about, if a double glazed/triple glazed unit gets broken how will you replace it.
I'm not sure about what you say about the triple glazing, but I offer the following in comparison.
I was in a poorly insulation 1960's house recently with one of the radiative temperature thingies you stick in your ear.
It was pretty cold outsite, 6 degrees or so.
The wall surface temperature was 14 degrees inside
The double glazed window in the kitchen with a 1mm uninsulated fabric sun blind was 18 degrees.
I agree with your comments about the differing climates, but I have had mixd experience with Iroko in Irish climate.
It is a fast growing hardwood and so the grain is not as dense - easier to work, less resistant to cracking/splitting on sites of severe exposure.
Also I understand it is a no-european timber.
You replace a double glazed window; -
(i) by the sealed unit, if the frame has removable beads
(ii) if not, by the unit frame if its in an open light
(iii) it not, by the whole window, if its a fixed light.