Since the days of SQL Server 7.0, if I've seen backups impacting a system in a way that affected performance, it was because there were already a bunch of other issues with the system that needed to be addressed. Backups by themselves, I've never seen them take a system down. I'd strongly suggest addressing all the other issues that are likely to be found in the system. Use wait statistics and gather query performance metrics to understand what is happening on the system.