As JW says the limit is defined by when you go vlock to block on your main, but before that happens you may find you've developed to much weather helm, making your boat hard to sail.
Hard to sail = slower, just to point that out
There are also some zany mathematics on how pressure distribution changes as the leading edge of a foil is raked aft, how it becomes more stall tolerant and loads of other stuff that is relatively "far out".
My thumb of rule on mast rake: Rake the mast aft until you can let go of the helm when going upwind in your dominant conditions and with crew/sails trimmed for best VMG.
We experimented with rake a lot while sailing the Tornado. For us the class standard ment that the rudder(s) at times was overloaded and lost grip. Then we had to sheet out to regain control. When we corrected this we became faster. We sailed at 200kgs crew weight which was not the norm. Find the setting that suits you and that is your setting
