I don't believe the IP address of the server affects SEO. However, the domain extension does. For example, .co.uk emphasizes targeting people in the UK, etc. You can also go to Google Webmaster Tools at www.google.com/webmasters/ where you can specify a country to target.
IP optimization is basically a part of networking where a person gets a live IP and makes variations in it in such a way that it can be distributed to several people for use.
and there is no such thing as you say as IP optimization for getting higher ranking in search results.
but yes you can always set your geographic location in Google Webmaster Tool if you want to rank higher in US
IP optimization is a process of the company to program their resources to be able to take full advantage of the IP resource value of the company. Company make use of this IP optimization to help them differentiate and arrange for their IP security purposes only. So, IP optimization has no relevance in terms of getting higher position for USA in SERP.