I've yet to beat this game on impossible. I can beat it on hard with every race I think, but the silicoids are hands down the easiest since you can colonize every planet and you don't waste precious production on cleaning. I think Psilons come next.

I need some tips on impossible though, been going with Silicoids here on medium or large galaxy, but at least one other race gets superior by far, and wipes me eventually. I've been wondering about restarting the game over and over until I get a favorable starting position on a medium galaxy, that should work.

-Any tips?
-What race? Can any race trumph the silicoids?

Silicoids is a good race, but check this comparision, I think that pros and cons of all races are correctly summarized there. (Silicoids are best at the beggining of game, but in late game they are losing in population race , and everybody hating them cause they were winning at beggining)

More important tips:
-always have at least 1 true friend - in late game the galaxy tend to split into 2 enemy camps and you dont want to be left outside of them.
-winning by voting is the easiest - aim for that
-at the beggining of game try to colonize as much as you can -> then defend / poke enemy with small-missle ship - low life and defense but great punch (only in late game switch to medium laser ship, with +2 range stuff and computers). (also keep 20 - 30 defense on your fringe planets, but dont bother on building it where enemy wont reach).
- pay attention to shield lvl of your enemies, it might happen that your missles wont be able to penetrate their planet shield, so it might wise to keep 1 strong bomb on your 'missle boats' just in case
- if you have 'rich'/ 'very rich' dont bother with science there, just crank up ships; and remember that on 'very rich' world your 'funding' will net you '50%' of credits you inversted so always 'fund' the 'very rich' worlds (you can fund your planets in menu where you can see list of your planets, i dont remeber right now where it was - in example if you fund planet A -100 credit the planet will gain 50 credit for production, and since very rich world have triple the production tha means for 50 credit you gained 150 production).

Thank you Thomas.

I started a new game on imposs right after reading this. Medium Galaxy with Silicoids.

For the first time I could just keep colonizing. I needed 1 Huge Colonizer for my 4th or 5th planet (extra fuel tanks) and I put everything from early research to parsec range 4, otherwise no problem, and thus I got hold of more than double the number of colonies of my largest opponent.

I think opponents have huge production bonuses on this diff, but mine is still the largest. I won on vote, but reloaded and kept playing to see if I can do a military win too, which I seemingly can.

I like best playing in medium or Large galaxy, but you're dependent upon having range to colonize.

Not on any difficulty does the computer players have the same range limitations on colonization as I do, is that correct?