Naas to Sandyford - avoid the Red Cow. If you are early enough (7am), you can come off at Citywest into Tallaght via fortunestown Lane and onto the M50 at the Tallaght sliproad (N81). The M50 itself is slow moving from there to Dundrum for some odd reason, but eases up to allow quick access to the Leopardstown interchange for Sandyford. Should take an hour.
Alternatively, come off the Tallaght Bypass at Fruitfield factory towards Marlfield and Ellensborough and come out at Old Bawn, across to Firhouse and onto the M50 that way.
After 8am all the sliproads into Sandyford, especially the Drummartin link road are very busy. I avoid the drummartin link road at all times and find it handier to come off at the leopardstown interchange.