As a counter point to your counter point I've used a 2010 Macbook Pro as my primary laptop for years. I upgraded the RAM and added an SSD and it still run great

As a counter point to your counter point I've used a 2010 Macbook Pro as my primary laptop for years. I upgraded the RAM and added an SSD and it still run great at most tasks. A 2006 Mac Pro though? What issue is it giving you? Admittedly - the processor will no-doubt show some age. And it's not qualified for the latest releases of Mac OS in quite a while. But it had user upgradable RAM and disk drives. Throw your preferred distro of Linux on there and I imagine it would be a sufficiently capable machine.