1200mm or 4 feet would be ideal.

The minimum is 1219mm. By the way in your new design do you have a landing space to the left or right of your oven? If you opt for less distance maybe your designer should do some research on ovens that have doors that open side ways instead of top down.

Thanks :) Yeah decided to go with tile. So sand cement is ok over existing tiles if I prep them first? Only problem is, the new pad can only be about 30mm at it's thickest (leaving up to 15mm for tiles) otherwise it'll end up being higher than the hallway floor. So I either need to make the fall shallower or not bother with the waste and make it all level. If I made it level, could I use levelling compound at that thickness or would deck mud/sand cement be the best option? Also, should I be putting in mesh for strength? (I know I should (and will) ask the local hardware what they suggest, but it's great to have suggestions from the Houzz community also)

Thanks for your comments everyone. We've taken your advice (Luke and NH) and changed the island to a rectangle (1200 x 3000). We lose one breakfast bar seat but gain storage and dining room space plus it shortens the distances from the island to the cooktops. It also removes the need for a corner carousel. We're much happier with this result. Dairy_maid, we've done what you suggested and walked through some common tasks. Overall it works reasonably well although we may keep some coffee spoons and butter knives in the scullery drawers for morning toast and coffee. We've also invested in a "silent" rangehood which has the motor on the outside of the house behind the fridge and we've upgraded the scullery sink to one that is 600 x 400 (internal size). Fabrication starts tomorrow. Woohoo. Once again, thanks so much for taking the time to respond. The design has been significantly improved with your input.