Hi,
No, I don't have the problem with other Arturia synths. That's why I asked, the SEM V is the only one that gives me that heavy overload and I have an Intel Core 2 Quad Q8200 @2,33 GHz, which isn't bad in my opinion. I think that depends more on the ASIO4ALL v2 driver itself rather than from the CPU. And I tried to increase the buffer size to like 2048 samples and it got just a little better but still some presets like EpicBrass and some strings give me that overload when playing more than three keys for a chord. On three keys it gives me like 70% load...
I also have some other really "big" VSTi like Sylenth1, Nexus etc. and these don't give me such an overload, no matter how many keys I press at the same time.