The price of E4500 has dropped yesterday and it seems that it is now cheaper than E4400
Newegg.com - Intel Core 2 Duo E4500 Allendale 2.2GHz 2M shared L2 Cache LGA 775 Processor - Retail
Newegg.com - Intel Core 2 Duo E4400 Allendale 2.0GHz 2M shared L2 Cache LGA 775 Processor - Retail
And E4600 was released yesterday but it is still not available at newegg, but you can find it in other places.......
Newegg.com - Intel Core 2 Duo E4500 Allendale 2.2GHz 2M shared L2 Cache LGA 775 Processor - Retail
Newegg.com - Intel Core 2 Duo E4400 Allendale 2.0GHz 2M shared L2 Cache LGA 775 Processor - Retail
And E4600 was released yesterday but it is still not available at newegg, but you can find it in other places.......