If you give 40% to a designer, how much are you going to give to your biz dev person (when you need one in three months when your beta is done)?
If you both use equity to give to the biz dev and the biz dev requires more than 20% to retain, you just lost majority of your business. :(
40% is way too high for a designer.
Also, make damn sure you vest any equity you give out.
Remember, you can only give it away once, so do so sparingly.