Apologies if this has been covered before recently but the last through comparison I found was for the now severely aging RPi3 and 3-4 year old GPUs/CiSCs.
Has anyone done a cost vs. performance analysis of any of the more recent 8 core, 64 bit arm SBCs vs current GPUs/CISC setups? Compared to a Raspberry Pi 3 the newer generation of SBC's seem to get about %240 the performance with the same upfront cost ($35ish) but with a 2-3W higher power consumption (about 25% increase on average compared to my Rpi3's)

Link examples of these newer SBCs.

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I totally missed that I got a reply to this post for a good month :)
The most direct comparison to the Rpi3 that conforms to the stats I posted is the Nanopi Fire 3, http://nanopi.io/nanopi-Fire3.html .Same price, double the cores working roughly 20% faster per core on my systems. Then there's the Odroid Xu4 http://www.hardkernel.com/main/products/prdt_info.php?g_code=G143452239825 which is $60 but has 4 cores working at near 210% the speed of a RPI3 core and the remaining 4 working at the aforementioned 120% improvement for about the same gain per dollar. Then you have what seems about a million boards going for 20$ using the same A53 cores as the Rpi3 but clocked higher.

Just a single datapoint here. I thought the sbc concept was
interesting. (Not using rasbperry pi for seti: have a couple
doing record-keeping/control though).

I acquired an odroid-xu4 (16GiB eMMC disk, 4 core,2GiB ram, 2GhZ clock) and
finished the setup a day or so ago.
Preliminary results suggest that it will accumulate about
700-900 cobblestones per day total
across the 4 cores. One built-in 40mm fan
cooling the cpu.

Preliminary results indicate that Ubuntu-Mate 16.04
sees the 4 cores as 8 (some threading bios
setting) but (again, preliminary) it appears that
running more than 4 seti threads is not helpful.

A single core takes about 8 hours for each current
task it gets.

Power use is under 40 watts at 5V.

I had been running an old HP laptop (68 watts, 1 AMD core)
as an experiment (it took 4-5 hours per task)
but it was big/heavy at 17-inches and its screen and keyboard
were failing so I've junked it.

I decided that I should measure power instead
of just quoting the max power the ac-dc
converter can deliver.

Running seti (four tasks) its power
use bounces around between 11W
and 12.x watts.

I'll call it 12W.

I'm measuring the (12 W) power use at the wall plug
with a Brand Electronics Digital Power Meter.