To those that have experience with one, how big of a portable A/C unit do I need?

Well, Ive decided to get rid of my window unit and get a portable a/c unit. My room is about 12.5'x10'x9'...I have 4-600w HPS lights, which 3 i finally got around to cooling via my exhaust fan. That cooled the room down about 5 degrees, but its still 83 degress at the canopy of the plants...so my question is to those who have used portable a/c's....how big of one should i get? Id like to get my room preferably around 75-76, but would settle for 79-80. The window unit i have is 8,000 btu and is not doing the job, although is getting old.

Also, can i exhaust the portable a/c through a wall instead of window or would that end of damaging the walls? (water damage)

Thanks everyone!!!

A/C 's are measured in BTU rating you can roughly work it out at 350 BTU's per watt of light in a non CO2 enriched room. If you're using CO2 then less this by 10%. I would suggest ither a 12,000 or 15,000 BTU unit with built in dehumidifier. Can get for around £300. Venting through the wall is ok if you use an inline carbon filter over the outlet to remove the moisture.

Hope this help, Peace