1.3 GHz seems to be mid-2013 Haswell based machine with Intel HD 5000 graphics, the other one is probably mid-2012 Ivy-bridge one with Intel HD 4000.
- Haswell based CPU is about 5-10% faster than Ivy Bridge according to various benchmarks (so, all in all it should be comparable in terms of pure speed, but read further)
- Haswell chips make SSD drives run faster
- Intel HD 5000 is much better than 4000 (and that will give most significant boost to overall performance IMHO)
So, if all other specs are the same, I'd go for 1.3 Haswell one, the problem is that you never know what you'll get when buying refurbished machine.
Yes, the SSD is the main difference.
Your iMac has a 1TB 5400rpm SATA Hard Drive and this is what’s causing the bottleneck. The MacBook Pro, on the other hand, has a solid state drive that is multiple times faster. So, while the iMac may actually process things faster, loading apps and reading/writing data will be a lot slower. And, if it needs to use hard drive space when it needs more RAM, this will also significantly slow things down.
Achieving the same/better performance
Since your iMac has two Thunderbolt 3 (USB-C) ports that support speeds up to 40 Gbps (via Thunderbolt) and 10 Gbps (via USB 3.1 Gen 2), the easiest solution is to use an external SSD that’s connected via one of these ports and to install macOS instead. You would then use that drive as your main boot volume.
However, you would need to ensure that:
- it’s definitely an external SSD (and not just a hard drive)
- it supports either Thunderbolt or USB-C (i.e. USB 3.1) as its interface
Both of the above are critical if you’re wanting to improve speed. Thunderbolt models are still quite expensive, but you'll find USB-C / USB 3.1 models at reasonable prices.
NOTE: Do not get confused by USB 3 - this is not the same as USB 3.1. And remember, it needs to connect to one of the two Thunderbolt ports (not one of the USB ports).
Some examples of the types of external drives I mean are:
Once you have the drive you want, you will need to install macOS onto it and migrate your data.
Best Answer
It's quite simple from my perspective - The 15 inch CPU is superior in all respects over the 13 inch CPU:
Turbo Boost engages for operations where only one core is active. Starting at a lower GHz saves energy and battery and as long as the CPU can boost to a faster top level than a competing CPU - you get the best of both worlds - fuel efficiency at idle and top speed when needed.
So, for a simple task where the computer is doing one thing only - you would expect the 13 inch to ramp one core up to 3.1 GHz whereas the 15 inch would ramp up to 3.2 GHz. Bigger is better for that task. Plus a larger L3 cache will make some switching between tasks more efficient on the 15 inch model.
Now, if you have video processing or a mixed workload where tons of compute is waiting for the CPU. You have two cores running at 2.66 or 5.32 GHz of theoretical throughput compared to 4 cores at 2.0 or 8.00 GHz of throughput. Again, no task scales perfectly, but even with 10% overhead, the quad core processor wins. It would have to be a bizarre benchmark to show the dual core i5 out perform the quad core i7 for any task that engages multiple cores.
If you want another opinion, I would recommend this nice article by Marco Arment on trying to calculate which Mac Pro CPU choice works for various budgets and tasks:
In it, he doesn't explain why he feels the 15 inch MacBook Pro is so far superior to the 13 inch MacBook Pro and simply states it as fact. I generally agree with that due experience and seeing benchmarks/reviews I trust. My feeling is the current 15 inch logic board and supporting components are faster and of better specifications than what is put into the 13 inch model. If you can swing the cost and live with (or prefer) the larger physical size, get the 15 inch model. It's an excellent workstation in a portable form factor. For many tasks it benchmarks as fast as an iMac and even the new Mac Pro.
Personal note: The base $1299 13 inch model is no slouch - I work from one almost exclusively the last year and I'm never really waiting for it in practice. If you need to pinch pennies on the CPU, I'd con side any of the retina 13 inch models if it means you can afford AppleCare, an external monitor plus backup drive(s) and whatever software you need to be productive. Rather than invest in tons of extra CPU cycles that you may not really use or need to work day in and day out.