Stronger is better, bigger typically means stronger, but not always.
It used to be that in orer to increase the tie rod assembly strength you had to go to the larger tie rods because the semi to full split adjuster sleeve would flex more at the 9/16 size than at the 11/16 size. Since you can get solid steel or aluminum sleeves that do not flex like the OEM splt sleeves, you don't necessarily need to go larger to reduce any potential deflection in the tie rod assembly. Staying smaller reduces weight. However, since your'e not in the US, it may be easier/cheaper to go with a factory style 11/16 set.
IMO, you will gain more benefit in steering precision from gusseting the steering box mount than you will be going with larger tie rods.
