I checked out the Harpy a bit more to compare with the Dragon.
My Dragon save is on day 61 with nearly 1000 mana and 243 dracomana and is on turn 1660. I focused on self-impreg before working on the maidens. At this point I can Hyper myself, all Surface folks, Randy+ and I have spare to get discount on the rest
My Harpy save on the same day with 860 mana on turn 1260. I focused on Emily before working on maidens. At this point I can Hyper Emily and all Surface folks. I just finished getting the full discount on Randy.
The Dragon is faster not only because of the starting 15 dracomana but also because of its boosted self-impregnation. Regular impreg with max discount increases mana by 4%. Dragon gets 5% because she gets 1 mana on top of 1 dracomana per egg worth 100 mana. The simple outfit boosts that to 6.25%, and you can spend up to 480 mana on it. The Harpy penalty leaves her at 5% growth on self-impreg, barely more than her normal 4.8%.
But the Harpy spends less time juggling mana around to trigger dracomana conversion. She got to day 61 in 30% less turns and with much simpler maths to optimize her mana growth.
The Cat could reach 600 mana by that point, thanks to the Outfit bonus and the early boost to discounts. The Fox would follow behind, having no bonus, even her acclaimed fertility is behind the Dragon's.