I have Perlico broadband and it works fine. If it isn't working well for you, then the problem is either 1) ZyXEL router 2) line or 3) exchange. If it's 1) then changing provider and getting a new/different box may correct the problem but if it's 2) or 3) then switching providers won't do anything to correct that problem.
I believe that Perlico just resell EIRCOM's broadband offering and do not use unbundled lines/equipment and I presume the Vodafone (who now own Perlico) are doing the same - so if it's 2) or 3) above, then it really Eircom's problem and if you are with Perlico/Vodafone I would suspect the chances of getting it fixed are slim.
Why not try to ger Perlico to swap the router first?