In one of my last project I make a function to accept an IEnumerable<T> as parameter. I normally used this function with PublishingPageCollection. This collection inherits from QueryBasedCollection<PublishingPage> and so it is a IEnumerable. Unfortunately the SPListItemCollection it is not.
I didn’t want to change my method and I didn’t want to create an overload only for the type of parameters. Then…I remembered that LINQ is my friend 
…
You can directly convert an SPListItemCollection. Below an example…hope can help you…
using (SPWeb web = SPContext.Current.Site.OpenWeb("myweb"))
{
return web.Lists["MyList"].Items.Cast<SPListItem>().Select(item => item);
}
{
return web.Lists["MyList"].Items.Cast<SPListItem>().Select(item => item);
}
