Sri Lankan is currently managed by Emirates so you should be fine.....

However, the assumption that taking the bus will be too slow is probably incorrect as total journey time (5hrs) will be about 1hr longer than flying.

For a 7.25am flight, I suspect you'll be leaving the City Centre about 6am. This will have you land in KUL about 8.25am so if all goes to plan, by the time you get through the airport, look to be on a train about 9am and at the downtown station by 9.30am. You then still have a little way to go to get into the centre of things so should be good to go by 9.45-10am.

How about taking a bus one way and flying the other? That way you also get to see some of the scenery (if rubber plantations count) on the way...