Unless you are shooting a bow with high poundage(70 lbs) plus with nothing on the string except your nock point or string loop I dought you will be getting 250 fps plus.Some of todays "fast"bows might yield you this like the patriot,mighty mite,outback,switchback etc but dont get to excited over it,speed isnt everything,accuracy is.
40 yard shots are possible though if you are set up correctly,tuned to perfection and SHARP broadheads.If you hit where you aim you shouldent have any problems with a 40 yard shot if you are completly confident in yourself and your equipment.Try to shoot the highest poundage confortable and it will definately help with the speed factor which makes things easier in the yardage department,and will also give you the most K.E possible.
Like paul said,use light arrows,go with a min of 6 grains per inch to be comfy,try not to load the string up to much,if using a peep then dont be bothered with a kisser for example.The no-peep will be a definate plus but only if prefered.Stay away from peep sites with the rubber tubing,can loose up to 8 fps with it.
Just practice,tune your bow,use good sharp broadheads and any whitetail that walks buy at 35-40 yards is yours.
Remember though that deer will " jump the string " .Most deer are shot within 25 yards anyways