I don't have a lot of experience with the 5er but I know it's a bigger car ...so maybe go drive one again. Try parking the 5er and just concentrate on the overall feel. Park it next to your 435 and then jump between them a few times. The 5er is a bigger car than I want to drive, personally. I like the confines of the 3/4 series.
Looks are subjective, of course, but I think the 440 GC is just a stunner with the M Sport kit. The 5er doesn't seem as aggressive especially in the front. And if you are after a sportier driving experience, the 440 GC with the MPPSK is hard to beat.
Something you can try if you are indecisive is to build an Excel spreadsheet with a column for each car you're considering. (Don't forget to include your current ride, which you can buy out at the end of your lease.) Put in whatever is important to you in a car and then give each car a rating for that row(1-5, 1-10, etc). Be specific, could even be something as small as window up/down switch feel. Total up the scores at the end and see how big of a difference there is. The results may surprise you (or confirm what you already thought).
Another question to ask is, if the money were not a factor - e.g. each car was the same price - what would you get. (That almost always ends in me finding out I want the one that's more expensive and that I need to save up
).
Charles