SQL Server 2008 R2 Express high insert slowdown possibly due to PAGEIOLATCH_SH
PAGEIOLATCH_SH means a page is read from the disk. There must be more at play in your workload than just INSERTs.

Simply and cheaply put you need a non-Express instance, more RAM and a faster disk. The complex and more expensive answer is you need to fix the application so that it does not read that many pages (ie. it does not do table scans).