0.025 is fairly narrow - but realistically you are not going to physically be able to tell the difference between 0.025 and 0.026 - the human hand is not going to have the resolution of a thousandth of an inch.

0.029 will give you a better spark but only if your ignition can support that gap based on the boost pressure you are running.

(Keep in mind spark plug gaps are in hundredths of an inch, 0.25 as you mentioned is a full quarter of an inch and not an actual gap)