I base everything off my chosen arrow, then getting into the 270-280 fps range by adding weight while finding the spine/length/weight combo that flies best. Lately this has been 150 or just over on standard diameter gold tips (insert, 40gr weight, 100gr bh) and 150-175 on axis by using half outs (50-60g) sometimes a regular HIT, and 100 gr Broadhead.
I like 100 gr Broadheads because they are typically smaller profile and allow more options to find the right combo of arrow length, spine, total weight, speed and point weight.