Tech rate effect on gameplay

Hell yes. Fastest means that individual techs don't make much of a difference, even hull sizes don't have a big effect for long.

Slowest is like the old galciv1 "ship eras". Where you would research a new ship type, and destroy everything in your path. You CANNOT play catch-up with the slowest tech setting, since you will be crushed. If you get medium hulls before anyone else, you have an advantage, but odds are the AI has better weapons or defence. It makes every tech you research a real strategic decision, since you aren't going to be able to race up the tech tree two techs every turn if they counter your attack. If they counter you, you're really screwed unless you have a good trading partner.

It's incredible fun too.

I enjoy playing on slowest cause I like my games "Epic"
As Marcathonas says it does force you to really think about what you research since usually it takes (once you get going) 4+ turns for "normal" techs (i.e, techs that arent too cheap or too expensive for you at the moment).
Im really enjoying it and I doubt I'll ever play much on normal or god forbid fastest
I like being able to use the stuff I make for atleast a while, one of the reasons I liked to play on the "Marathon" setting in Civ 4, your armies weren't outdated when you finished building them and you could have a few wars with em before having to upgrade.
But I guess its not for everyone, you really need patience
Only times I did run fastest tech games were when I wanted to see what all the hull sizes looked like for the different races

Maybe im wrong with this but i played on fastest and normal and it was the same ... only slow and very slow seems to work

But I guess its not for everyone, you really need patience

Or a lot of free time on your hands. Some of us don't have that. I like games that I can finish in 2 hours a night for a week, or something that would only take one long playing session on Saturday or Sunday.

you can always save the game and come back to it later...