first time,
it may vary a little bit.
I know when I am working up a load the accuracy will vary when I put in a couple grains more or less powder and change the velocity accordingly.

You will need to shoot in the appx. temperatures you will be hunting in to fix your final sight in before you go hunting.

For longer range shots (over 300 yards) there will be definite difference in accuracy. The bullets impact on the target will impact higher or lower depending on the velocity changes. There will also be a slight difference in wind drift, again more noticeable at longer ranges.

Go to one of the ballistic information sites on the web and punch in your info and it will give you a readout on what happens when the velocity changes.
Go to www.biggameinfo.com.
Really cool site. Has a ballistics calculator, recoil calculator and some other cool stuff.