Hmmm..... should i wait..

A $200 price difference might not be worth it and the 7870 is a good enough card to give you top quality performance in most any game. Below are some benchmarks from some of todays populsr games and the settings are at ultra with a screen resolution of 1920x1080 so it will give you an idea of the max settings performance which can be adjusted to suit your needs.

http://www.guru3d.com/article/his-radeon-7870-iceq-turbo-review/16
http://www.guru3d.com/article/his-radeon-7870-iceq-turbo-review/17
http://www.guru3d.com/article/his-radeon-7870-iceq-turbo-review/19
http://www.guru3d.com/article/his-radeon-7870-iceq-turbo-review/21

From what i've heard the card is not overly large and should fit in your case. The size measurements are usually given with a card in the details of the card. The links below should give you a ballpark as to the measurements since the cards won't deviate much from reference.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814150586
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127645
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150591