Better with a thunderbolt drive like a LaCie rugged. Get full speed on the SATA connection. The only faults of these machines are the lack of USB3 and the bad, cracking solder on the GPUs.
I’ve had the GPU replaced once in the recall, and subsequently twice had to extract the GPU and bake in the oven for ten minutes to remelt the solder together.
Whoops, I meant to say Thunderbolt drive instead of Firewire. Yes, the external SSD solution works well. Though for me I did it so late in the machine's life that I went with a cheap small SSD. My GPU is working fine since I got it replaced in the recall. But I'm ready to move on and not risk it. Plan is to retire the machine once the new iMacs come out. It will be seven years old and I've gotten enough value out of it. I also "deserve" to use something current. I figure going 7 years is frugal enough.