I do not know if I would change a thing with your setup. 258 fps isn't a bad number when you consider the distances most deer are shot at...especially in the eastern part of the country. Most of my hunting setups still average in the 265-275 fps range because I have found it offers the best compromise between a relatively flat trajectory and decent KE/penetration. (not sacrificing a smooth draw or low recoil in the process)

Going lighter with your arrow weight may increase speed (though how much of a flatter trajectory will be obtained is questionable) but you will start losing Kinetic energy thus your penetration potential will go down. Really the only way to increase speed and not lose penetration is to bump up your draw weight. Again though, moving it up to 70 lbs will only net you about 7-8 fps. That will increase KE noticeably but the flatness of your trajectory will, again, only get marginally better.

Out of curiousity, what string accessories do you have installed? Depending on what you have installed and where they are installed you can lose quite a bit of speed. Ultimately though accuracy is the most important issue for most archers today. If your setup produces decent speed, decent penetration and good accuracy then I would not try to change a thing because you may lose some of the latter.

Hope this was somewhat helpful.