Cubic Desktop

Split A / C room selection for the office?
I have to install the split air conditioner in the office of my brother. It is 250 square meters with 11 m in height. He has 10 people on their desktop computers and light tube 5 of 40 W. On the basis of the calculation of the cooling load of 4.5 kW peak. But I could not get all the data to estimate the burden of the solar radiation and infiltration load. Also CMM (cubic meters per minute) air, I calculated from my book came out at 3, so that all CAs have MMC in the range of 14-16 is my calculation correct? Now with AC 6000W, 6250W and 6600W are available. Which should I choose? I thought the 6250W one.
There are many factors to consider and information is always difficult to be advised. The capabilities are not differ much, so I would go for the largest being the right side.
What a beautiful 3D desktop