Hi sinky,
On the cost comparison between the two, using this mortgage calculator
http://www.drcalculator.com/mortgage/ie/ (and assuming a 25 year term, you start repaying in May and there are no rate changes in 2014)
4.3
Monthly repayment: €762.36
Cost of interest up to end of 2014: 3986.99
4.5
Monthly repayment: €778.17
Cost of interest up to end of 2014: 4173.22
At a rate of 4.3% over the lifetime of a 25 year mortgage (and assuming nothing changes... highly unlikely!) the interest amounts to €88,707.48
At a rate of 4.5%, the comparable amount is 93,449.64
I would suggest playing around with the calculator a bit yourself to see how the different scenarios pan out and work out whether the BoI sweetener is worth the higher interest cost and the higher monthly repayment.
On whether or not to fix, that has to depend on whether you want certainty in your payments for the fixed period. Fixed interest rate comes at a premium as the bank is taking on the risk of its cost of financing going up it will generally set the rate to account for some fluctuations. In general don't fix unless you need that certainty, it ties you to the rate (great if it rises, not so great if it doesn't) and it usually limits or penalises you repaying early.