I have arduino 2560mega and 3.2 TFT display, but this constoller is too slow for me, i need something faster. I think this is impossible but 500mHz clock would be Exelent.
Actually, at this point I'm betting that what is too slow for you is the display updates.
While the speed of the processor can and normally does affect things like display update rates,
it is not the only source of overhead in updating a display.
There are many sources of overhead that introduce latency which translates into a lower output performance.
It could be the use of floating point math, it could be the low level hardware interface is slow, or
it could be that the low level code is overly conservative and is inserting longer delays than is necessary.
Anytime you start to want more performance out of a system, you have to look at the entire
system and optimize the system as a whole.
For example, if the majority of the added latency is due to a slow communications interface or extra
conservative delays in the low level code, than boosting the speed of processor will not up
the performance very much, if any.
The solution to increasing performance depends on where the overhead exists in the current system.
Until you break down the problem a bit more and look a bit closer into the actual overheads,
it is not a given that a faster processor will ever meet your expectations.
Likewise it is possible that changes to the code when running on the existing processor
could speed things up significantly.