The coverage from the 1200's would probably suffice, however, you state that there will be approx 150 users, per floor? I can guarantee you that if you try to put 150 users through one access point, the reseults won't be pretty, and you may find yourself jobless the next day.
your going to run into a lot of problems with the solution you need, particularly with the oval shaped office, and the required number of clients.
The first thing you need to check is if you have leakage from floor to floor, use a directional patch antennae and try it in various positions around the wall of the office, use the cisco site survey tool to check if you receive a signal on the floor above.
You need to design very carefully so as to avoid any channels overlapping with each other. This usually means that access points nearby (above, below or each side) will need to be on a non-pverlapping channel. For 150 users per floor, I would recommend using approx 10 access points. Use a mixture of the 2.4Ghz and 5Ghz ranges to avoid overlapping and use directional antennaes on a lower power to keep the coverage controlled.
Get a site survey done as well, but try and do some background checks on the company you use.. I used our silver partner to do our survey and was very dissapointed when they provided me with a solution that would not work and wasn't what I had asked for.
