Thanks for the comments. I hadn't even though about getting rid of the horizontal mullion, it was drawn like that in the plans by the architect not sure why and then the windows were priced based on this. We have two other windows with the horizontal mullion so I will ask them to get rid of this, dunno why I hadn't thought of that. Good point though, thanks for that.
I actually emailed Internorm after I posted this and asked could I do the big window in one piece, they said they can make it as one window so think we are going to go with that.