C# - Create A Business Model Wrapper For A Generic Database Approach?

I'm currently facing a performance problem with creating POCO objects from my database. I'm using Entity Framework 4 as OR-Mapper. The whole application is a prototype for now. Let's assume I want to have some business objects like classes 'Printer' or 'Scanner'. Both classes inherit from a BaseClass called Product.
The business classes exist.

I try to use a more generic database approach. I don't want to create tables for "Printer" nor "Scanner". I want to have 3 tables: One called Product, and the other Property and PropertyValue (which stores all assigned values to a specific Product). In my business layer I do create a specific object like this:

public Printer GetPrinter(int IDProduct)
{
Printer item = new Printer();
// get the product object with EF
// get all PropertyValues
// (with Reflection) foreach property in item.GetType().GetProperties
// {
// property.SetValue("specific value")
// }
return item;
}

This is how the EF model looks like: Works fine so far. For now I'm doing performance tests for retrieving multiple sets. I've created a prototype and improved it several times to increase the performance. It is still far away from being usable. I takes 919ms to create 300 objects who only contain 3 properties. The reason for choosing such DB design is to have a generic database design. Adding new properties should only be done in the business model.

Am I just being too stupid to create a performant way of retrieving xx objects or is my approach totally wrong? As far as I understand OR-Mapper, they are basically doing the same?