I like the conversation here and elsewhere on research speeds. In my games, my choice of research speeds has tended to yield the following results, which are quite similar to those nuclearslurpee reviewed above.
100% research speed:
* rapid research growth until early to mid-fusion level drive; getting antimatter drives is quite time-consuming. Precursors aren't too much trouble, the Swarm can be a bit of a nuisance, and Invaders are deadly but at least sometimes survivable.
10-20% research speed:
* similar research slowdown, except "ion drives are the new fusion drives, and mid-level fusion is the new antimatter". Like nuclearslurpee said, tech advances still (depending on start tech) usually starts off relatively fast and slow down, just more quickly, and bog down at a lower level. Therefore, space is vaster, the Precursors get vastly harder to beat, the Swarm is extremely dangerous, and Invaders are death once they find you.
I have never much liked either the rapid rate of tech advance in the early game, nor the near-stasis in tech advance later on. When attempting to solve this issue, one runs into another: several of the AI factions in Aurora - Precursors, the Swarm, Rakhas, and the Invaders - each seem to have fixed tech levels, and therefore are either impossibly murderous or boring if player tech is very much different.
Each of them, in fact, are most interesting to play against in a game in which player tech plateaus at a consistent point, and therefore Research Speed (RS) is (at least approximately) a given value, one presumably playtested by Steve.
The Precursors start off with a higher tech than most player empires do, then lose this advantage over time at a rate dependent on the RS setting. Set this to 100%, and it's quite easy for your first serious fleet built after game start to be able to outfight many Precursor flotillas. Set RS to 20% or less, and the Precursors will only slowly be a thing you can actually do something other than run away from. Same thing with the Rakhas.
In a game played mostly against the Precursors (which is a pretty good option for those of us without beefy CPUs), I'd set Research Speed to between 10 and 40%, with the lower value for highly experienced players (especially if starting on Sol) and the higher value for newbies, or those desiring a quicker game (and with a little bump if your empire does not start on Sol).
The Swarm spreads - that's a big difference. The lower you set RS, the more dangerous and even potentially civilization-starving the Swarm can be. I've actually lost a low-RS empire to the Swarm once.
For games played mostly against the Swarm, I'd try RS values of between 20 and 40%.
The Invaders are very different again. They don't just have a much higher tech level, they expand even more vigorously than the Swarm. Include Invaders in your game, set RS too low, get unlikely with the placement of activated wormholes ...
and you have a game that no player can win ...
and it'll take you tens of hours of gameplay to find out you were doomed from the start!
Games played mostly against the Invaders are very chancy. It's all about how quickly they discover you, and how effectively they can bring firepower to blow up your civilian craft, block your trade routes, and kill your warfleets. While you can design games where you expect to fight sooner, or later, wormhole placement is very random.
For games played mostly against the Invaders, I'd try a Research Speed of 100% or more, unless I parked my empire homeworld well out of the expected line of fire.
Regular NPR empires are more flexible, as they do gain tech over time. However, the AI tends not to prioritize or optimize research, or optimize planet facilities, or ship design, as much as an experienced player does. Therefore, the higher the RS value, the more quickly you are likely to outpace AI players, unless you've given them sufficient research (and resource, and perhaps other) bonuses.
For games played mostly against other empires, Research Speeds of anything between (at least) 10% and 100% can be got to work well.
However, if one desires the rate of tech progression to remain more constant than is usually the case in Aurora, and instead experience an epic game against AI empires where one stays at fairly low tech for some time, and yet eventually can field - and fight against - some *truly* advanced ships, one might consider starting the game at a Research Speed (RS) of 20%, and proceed to multiply the current RS by 115% every decade (rounded to the nearest integer %), with no upper limit.
RS years since game start
20 0
23 10
26 20
30 30
35 40
40 50
46 60
53 70
61 80
70 90
81 100
93 110
107 120
123 130
142 140
163 150
187 160
215 170
248 180
285 190
327 200
376 210
433 220
498 230
573 240
658 250
757 260
871 270
1001 280
1152 290
1324 300
1523 310
1751 320
2014 330
2316 340
2664 350
3063 360
3522 370
4051 380
4658 390
5357 400