These are dual capacitors, the 35 and forty signify the compressor side, and the 5 is for the fan. If you use the new cap, you will be using the wrong size for the compressor. Either keep the old cap and only use the herm (compressor side), and get a separate 5mfd for the fan, or get the correct dual cap which would be just like the old one, except it would be, well, new.
Now, that being said, if you actually had the old cap tested, and it is indeed within range, then you are probably safe reusing it. I always replace caps when changing motors, but that's because I have to warranty my work, and its just a good practice for a professional. Capacitors are fairly cheap and easy to replace. I have seen people replace a motor, only to find out it was just a five dollar cap that was bad. Now that hurts.