No, it would not kill your N900.

In theory, it is better than scaling because:

1) higher frequency saves more energy - I am lazy to repeat all my measurement which shows that but you can browse this thread back.

2) no switching - no expenses on switching.

3) fast reaction.

But my measurements show that there is one disadvantage -

ARM has two VDD and VDD2 is used to power peripherals (bus, SGX etc). And it needs to be powered more with higher frequency. So, the energy consumption on high frequency is a little more in practice - in simple CPU intensive calculation it gives a better result but in case of day-to-day usage the peripherals eat this advantage.

However, it is not big and you may try in your N900, especially with different voltage setup.