But what are you using it for?
For games the 4550 is a total waste of time, but it is perfect for genaral office work and HTPC applications.
Unless it is cheap there are better cards than the 3870 for games, the HD4770 is a good deal faster and can be found for just under $100 at the Egg with rebates and the HD4670 is as fast as the 3870 while using far less power and is under $60 again at the Egg, with rebates.
If you have a 3870, keep it. 3870 is much better than 4550. Unless you plan to get an 48XX series card. Bottom line is 3870 is better here. HD3870 512MB 256-bit GDDR4 320 Stream Processors. Only thing as good would be a 4670. Hope that helps.
^Well you can get 2 4770s for less than the price of a single 4890 and get better performance than the 4890...
http://www.tomshardware.com/reviews/radeon-4770-crossfire,2288.html
woah! thanks for the info! Never knew that 4770 was another card i could consider! Great find mate!