People who think they need such high doses of B6 may in fact not be converting it properly to its active form pyridoxal 5 phosphate. This is an enzyme controlled action, requiring B2 Riboflavin as a cofactor. Some drugs and genetic conditions also lead to poor conversion.

This may be avoided and high dose not as necessary by using P5P tablets (enteric coated) instead. Even the high dose pyroluria treatments use only about 50mg of P5P version when doing that.
NOW company makes a nice version that is affordable.

more on pyroluria here:
http://www.drkaslow.com/html/pyroluria.html

Signs of high dose B6 toxicity are balance problems, and numbness in the extremities. It is typically time dependent so long term use is more likely to create problems than shorter dosing spans. But we have had people come on the PN forum complaining of doses of 100mg daily, over the years.
So keep that in mind. Some people just can't handle the high doses. If by coincidence you are pyroluric, the high doses won't affect you the same way.