PC2700 isn't DDR-400......PC3200 is So 200mhz x 2 = 400 with PC3200. But since yours is 2700, 183 x 2 = 366, so it's correct. CPU-Z is right. You're simply mistaken in your assumption, no big deal man.
As for what to set it at, it depends what brand it is, and what timings it is rated for. For example, is it 3-3-3-8? Or 2.5-3-3-3-7? Or 2-3-3-6? etc.......
Find out that info and then someone can help. Although, would also help to know what mobo, just in case.
There's more out there, but it gets REALLY technical. Suffice it to say that, generally speaking, lower RAM timings are better. But that means the RAM is better and has to be able to perform at those faster timings. Not all RAM is created equal....just like cars The best DDR RAM runs around 2-3-3-5 @ 1T.
DDR 400 (PC3200) runs at 200MHz external clock if your processor is running that fast an external clock too. Your mobo, processor and ram all have maximum rated FSB's and the lowest of these is what you can actually run at synchronously without overclocking.
For example despite my DDR400 ram, my Athlon XP 2800+ runs at 166MHz external x 12.5 multiplier so my ram naturally follows suit at 166 (333MHz DDR). I can set the ram to 400MHz in the BIOS since it supports that & so does the mobo, but this is asynchronous with the FSB and actually makes the comp slightly slower in my tests.
The asynchronous bit means that instead of each cycle in the 166MHz passing data from the ram to the cpu (synchronous), the ram goes on a faster ratio (6/5) and provides data for the bus at this off-beat frequency.