hi!
Yes you can use PBR to achieve the result you have described.
The following link gives details on how to configure PBR and the steps and required sample config.
http://www.informit.com/content/images/1587050722/samplechapter/1587050722content.pdf
Refer page 35 in the above pdf for PBR explanation and sample configuration.
In brief , you will have to,
1.create access list(acl 1) to match 3x traffic.
2. Create an access list(acl 2) to match 5x traffic.
3. Create a route map with 1st permit statement and match ACL 1. Set the "ip default-interface" to T1, or you can set "ip next-hop" to ISP1's ip.
4. Repeat the above step for ACL 2 creating another permit entry in the route map.
And lastly you have to apply the route map on the interface for PBR.
Please revert if you have any queries further on this.
Regards,
Niranjan
(pls rate if helpful)