I've got a TDK 40/12/48 and I buy cheep disks that are only rated at 16x so I never (except once to test it) run the 40x at over 16x. At 16x a full cd is taking under 6min which is fast enough for me. At 24x you are looking at under 4min.
The point is that I think a 24/10/40 is fast enough so don't make up your mind based on speed.
BTW I have an 8x Phillips that I hate because it only works good at 4x which takes almost half and hour. I really like my TDK, no coasters yet!
Give me fuel, give me fire, give me that which I desire.