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I had some time on a long car trip and made a spreadsheet to do some figuring for an optimal way to boost chemical energy storage.
After I got some interesting numbers out, I was able to wrangle them into an over-unity device. (Sadly not a perpetual motion machine since it can't use the rocket fuel as an input)

Now you can run your trains both FASTER and FURTHER on the same amount of fuel!

The circuit network is rigged to power up the factory and beacons when the input chests are sufficiently full to guarantee both factories have feedstock and the output chests are not overfull. Until then, only the inserters pulling the completed rocket fuel out are powered by the large poles.
Inputs:
2500 MJ worth of solid fuel (100 cubes)
254 203 MJ electricity for beacons (0.48MW * 6 beacons * 8.82s /1.25 crafting speed * 5 iterations / 50% boiler efficiency)
310 248 MJ electricity for assembly machine (0.21MW * 2 * 840% * 8.82s /1.25 crafting speed * 5 iterations / 50% boiler efficiency)
<1 MJ electricity for inserters and circuit network
------
2952 MJ (~283 225MJ of which is electrical losses due to boiler inefficiency)

Time: 88 70 seconds

Outputs:
3150 MJ worth of rocket fuel (14 boosters)

Net Gain:
198 MJ (423 MJ if using solar)

Solid->Rocket Fuel Conversion Efficiency:
107% (Boilers)
116% (Solar)
NOTE:
If there is an arrangement of beacons which allows a 7th to boost both factories, that will be even more efficient.
Using 8 beacons to impart 7 effects reduces efficiency.

EDIT:
Math did not include the 1.25 base crafting speed of the assembly machine.

If you tile this vertically, it would have an even bigger gain (it looks like just over 40 additional for each sharing the side - 80 mw total).

The most efficient layout is an infinite square alternating rows of assembling machines and beacons.

Updated:
Math fix - assembly machine works 25% faster than assumed, saving energy and driving up the efficiency by a few more percent.