I've tried this with Siam on Fractal, Immortal, standard. Science victory on turn 240 which is my personal record. I was able to hardbuild two settlers and rushbuy the third because my capital had 4 sheep tiles, two plains wheats and the rest were hills. Huge production potential but only a little amount of food. Got the NC around turn 85, used the "+15% growth when not at war" and interfaith dialogue + mosque of djenne + cheaper missionaries. Due to early alliances with cultural city states and Siam's UA I picked four policies in Patronage and allied basically every city state on the map which gave me an additional 100+ science and an insane amount of growth, culture and faith. Three observatories did the rest. Also three maritime city states, Siam's UA and +15% growth was pretty hilarious. All my cities had +20 pop on turn 200 on a map without any grassland or rivers. xD Overall, I don't think a wide empire can beat this strategy in quickest science VC. I've played a pretty flawless game with Russia and had 13 cities on turn 100 with great production and early aqueducts. On turn 240 I had 2000 per turn but it was too late. "Only" won on turn 260. It's certainly much harder than going tall.