Assuming you are on the PAYE system, you would need to consider the age related maximum Employee Contribution Amounts.
The max pension contributions you can make are limited to a % of your total PAYE income.
Check here:
This page outlines the tax relief for pension contributions
www.revenue.ie
Assuming you are aware of these limits,and are within those limits to get PAYE free contributions, a salary increase of 10k, being put into a penaion scheme, will only be subject to Employee PRSI & Employee USC at your marginal (highest) USC rate.
Typically, a salary increase is subject to 4% PRSI, and 8% USC if your total PAYE income exceeds 70k annually.
So putting in all of a 10k salary increase, to pension, will reduce your nett pay by €1.200 annually. (USC & PRSI apply, of a combined 12%)
However, there are other options, if you setup a Company Scheme, where the Company contributions made, have no PRSI, USC impacts on your nett pay, but company contributions also have restrictions, allthough these are generous
Some professional advice would be needed to setup such a Company pension scheme