I'm planning an island in our kitchen renovation and it sounds like you have plenty of space. We have 48 inches at our ends and then 84 inches to split for the parallel sides. My island is currently 8.5 feet by 42 inches.... I could reduce to 36 inches wide and then have 90 inches to split. Although I really like the look of 42 inch wide. If you live close to ikea that is a good spot to go view kitchens with varying isle space. 40 inches looks plenty to me and 42 is huge. If your wall us gone get boxes and map it out. You really need to a visual. Good luck! Let us know what you de use.

Try putting painters tape on the floor in the size and position of the proposed island and then mimic your usual kitchen activities to see if the measurements are right. We did this for an entryway/bathroom redo and found it helpful.

How did it come out? Can you attach pictures? I have a similar situation. I removed the dining room wall and installed a new kitchen. Now that the cabinets are in, I have 8 ft. of space between each side of the kitchen. It seems almost too much space so I'm thinking of adding an island but I'm concerned about doing it. I'm looking for others on HOUZZ that might have done this successfully, before attempting it. Thanks!