If the OP has a draw weight of 60 lbs and draw length of 28" (as said in his post) I'd say his speed is pretty close to what should be expected. My lighter weight arrows are also 450 grains and with my DW being 63 lbs and DL being 29" these are shooting (measured through a chronograph) at 280 fps. My additional 3 lbs DW and 1" DL making the difference, in my estimation.
One thing the OP might also want to consider is that shooting heavier arrows will make for a quieter shooting setup AND his arrows will retail more down-range energy for increased penetration potential. If he's truly going after BIG game, such as elk and similar size critters, his 450 grain arrows would be a better choice than something lighter, just for the sake of getting a little faster initial out of the bow velocity, IMO. Faster, lighter arrows lose more speed over distance than do heavier arrows. That's just a fact that follows the laws of physics.
There are several online articles as well as in hard print, about the pros and cons of light vs heavy arrows. He might benefit from checking into this before buying light arrows - he just might determine what he has are a good choice and save some money too.
2008 Martin Firecat Pro-X (29" DL, 66# DW), home-made TRG, new VEMs, DS Advantage/HHA Pro-5519 front sight, No-Peep Sight Eliminator, Limb-Driver arrow rest, B-Stinger stabilizer/dampener, custom upper STS, G5 Head-Loc quiver on custom mounting bracket. Gold Tip Velocity XT300 arrows with Bi-Delta 2.5" Sharkstooth vanes and Grizzly single-bevel broadheads, 498 grains at 262 fps (22% FOC)