Use Karl Jeacle's mortgage calculator to calculate the potential long term savings available by switching assuming that the price differential between lender's remains constant into the future.
If using from locations (work) where you're unable to download, lots of other mortgage calc's available (google "mortgage calculator) that should work for you. Most of the lending institutions are now offering them. A few available here.
The big difference here may come from the additional payments. Do you often pay off small amounts extra on the mortgage? Would most of your over payments be over the €1k limit from BoSI?
If you often are able to add €200 or €400 payments, but seldom get that figure to over €1k (some people find it hard to save up small payments into large ones and end up spending the savings in the mean time) then you'll probably save more than the 1 year reduction in term using the overpayments with no limits on your current mortgage.
It's impossible to tell which rate will be better over the life of the mortgage (though you are only really concerned with the short term as you can switch again in a couple of years time if a better rate is available) so minimising the interest payable in the time you are with this mortgage/rate is the key aim.
Look at your budget for the future as you see it. Try out the different rates and the assumed payments over a year/2 years/5 years with both lenders (taking into account the 1k min with BoSI) and using a mortgage calc (Jeacle or any other calc out there) see which one might be better for your situation.
If you often are able to add €200 or €400 payments, .... then you'll probably save more than the 1 year reduction in term using the overpayments with no limits on your current mortgage.
this is exactly what i was thinking Setanta! thanks very much!