300-350 is ok on 94+ Miatas with LSDs. The big enemy is wheelhop. I have had my 4:10 torsen from my 96 put in my 99 and its got about 250k on it with no problems *knocks on wood*. But then again, i am only at about 200hp also. There are a few guys on miata.net who are running these numbers... you should go on there and ask also.