Also, at the minimum, i would add more ram. If you have to use the old machine, a ssd might do you some good. You may not get amazing throughput, but the access times will make using the older machine for production more tolerable, and might even make it feel twice as fast.
The steps you should take:
1. Add ram to both. 4GB would be my minimum.
2. BACKUP your data. i cant say how important this is.
3. Seriously consider an SSD. You wouldnt need a big one. 50-64 GB should be fine for your OS. Save your crucial data onto an external drive, and then BACK THE EXTERNAL DATA UP.