Speed is the least of your worries when bowhunting as long as you' re using fairly modern equipment, such as a compound bow.
I' d be more concerned with draw weight and total arrow weight, which includes your broadhead. A 55# bow and a minimum 400grn total arrow wt. This setup would be adequate for elk to 35yds. Yes you can take elk with less poundage, but it is not recommended and it would be less than adequate, especially for a first time hunter. If you can pull a little more poundage, then that would be a plus, especially on marginal shots where a little more umph can make a difference.
Make sure equipment is well tuned, with a good quality Broadhead such as Muzzys--Thunderheads--Magnus etc. Make sure you do your part as far as practicing goes, and it' ll give you total confidence in your equipment, the rest is up to you. Good Luck. elknut1