Ah. Huge (and large) maps have a increase in tech price built in that makes it harder to research fast for a given size/efficiency of civ. You could give it a try on a standard or small map and see how you do - I know from experience that it's possible to get to 4 turns per tech in the late middle ages and stay there on regent (small map).
Also, the lone scientist thing - yes, strange, but can be very useful if you want to do a 40 turn research on something and you happen to have a useless citizen sitting around somewhere (you know the kind in semicorrupt cities where you're already at size six, don't feel like paying for an aqueduct, and whether or not the last citizen is working a tile makes no difference to anything besides food). Just be careful - under certain conditions (I'm not sure exactly what they are), the governor will change the scientist to an entertainer on you, so you need to keep an eye on it.)
Renata