I'm neither a M40i or 35i owner, but a 28i owner!
Coming from the "opposite" end of the spectrum I would highly recommend the M40i. Sure, you might have to spend a couple thousand more, but I assure you it will be a much more financially responsible decision than getting a 35i and selling it in a few months to get the M40i.
Not saying that you would, but it IS something I am agonizing over right now....