when you mount a fmic will you have boost lag and lower boost ?

 

You will get a little bit of lag, maybe 0.2 sec or so, depending on your setup. The boost should remain the same, but you will get more power for a given boost level because of the cooler air.

I highly recommend spending $3 on The Spearco Catalog if you are considering an intercooler upgrade. The Spearco Catalog will show what to look for in an intercooler so that you can make a better decision when selecting one for your car, regardless of the intercooler brands that you are considering.
http://www.spearcointercoolers.com/

Edit - While talking to someone else about this subject today, I think that I understand your question about the boost level a bit better. If you are asking about pressure drop, then yes, more tubing bends will cause more of a pressure drop. However, whether or not you have more total pressure drop than the stock IC depends a lot on your intercooler core, end tanks, and plumbing. See the Spearco Catalog for a better understanding of the core's pressure drop in relation to boost and flow rate. Also, Corky Bell's "Maximum Boost" and "Superharged!" books also address this issue, although I'm not sure if I agree with everything in his books.