I have a 370fps crossbow and I'd like to get the best bolts for speed and accuracy at 50 yards and in. Any opinions on length, weight, fletching style and arrow brand will be appreciated.

Crossbows are generally made for 16, 18, 20 or 22 inch bolts, use the length for your bow. Just like with an arrow for compound bows weight forward is a good thing for bolts. Parker Red Hot and Carbon express Pile Drivers are 2 that are weight forward. Generally a heavier bolt will yield better accuracy and reduce noise a little, slows it down a little but it is plenty fast to hunt anything in this country.

On tip weight I get better accuracy with 125gr tips than 100gr, helps improve weight forward of the bolt and increases weight.

In my Parker that shoots 330fps with the redhot 20 inch 2 inch groups at 70 yards is the norm.

What brand crossbow? What length arrow came with it? You can get some good arrows from Deer Crossing Archery (and get a 10% discount using code Joe53). Or, you can call South shore Archery and have Jerry custom make some Black Eagle arrows that are spine matched and weighed. They are probably the "best" for long range accuracy. For hunting accuracy - out to 40 yards or so, I have not found enough difference in accuracy to warrant the price. You might see differently. It is easy to robin hood at 40 yards if you shoot at the same spot twice on a regular basis (ask me how I know).

I have arrows with both 3" and 4" vanes. The 3" look sexier, are lighter, and add a small bit of speed, but I prefer the 4" as it just seems to give me a touch better accuracy. Arrows in the 325+/- grain range are considered the sweet spot for most bows. I have them ranging from 300 to 400 grains using a 100 grain point. Heavier is slower and has more drop, but penetrates better, which doesn't matter on deer as you will shoot thru almost always on a proper shot.

Length and nock type is dependent on brand of bow.