Longer bars the changes are not as brutal.
Shorter bars the changes get very brutal.
Averages usually run 20 inches to 22 inches center to center. I have seen 28 inches. I have seen much shorter in lower powered cars.
If you are using pre-made brackets by all means use the same maker for front and rear brackets. Find from them how long of bars those brackets are designed for. Also question them heavily about you getting the rear and front brackets lined up up and down, like the brackets were designed.
Ed