Getting 6 hours while recording would be very impressive but probably not going to happen, good thing is where there are amps to be plugged in there power outlet's for a computer. Do you know what software there is available to you?
Processor does some what matter but the big thing when recording is memory. Would recommend no less then 4 GB of memory, but 6 GB would be nice.
I use Ubuntu for my OS and I use a Digital workstation called Ardour but it only runs on Linux systems and OSX.
If you want to run Windows yes there is pro tools but if you want something free LMMS which runs on Linux but there is a version available for Winodws.
My Windows PC recommendation.
http://www.newegg.com/Product/Product.aspx?Item=N82E16834230075
This one is of great quality build and will have all the power you need.
A Linux (Ubuntu) recommendation
http://www.system76.com/product_info.php?cPath=28&products_id=118
I do recommend this one, easy to use OS, handles the two programs listed above amazingly being that it is a "Unix Like" OS and the company has great reviews for quality. I would though recommend that if you get this model configure it with the 2.5 GHz i5, 6 GB of memory and the 500 GB Hard Drive which bring you to a total of $873
If you decide no on both these models just stick with a i5, 4-6 GB of RAM (preferably 6 GB), and as far as good brands that are quality built from Windows ASUS, Lenovo Thinkpad, Sony Vaio, Samsung. Any of these can run Ubuntu.
From a Ubuntu Models you have System76 I showed you and Zareason.
good luck shopping and do tell us what you find, if I may ask what do you play and what kind of music if you do not mind me asking.