Rémi, portinfer;
It's very hard to give advices about fins but I can give you my own data and what fins I think is too hard and too soft:
1. 75kg
2. 178cm
3. Trained athlete but not very strong
4. Kicking whith almost straight legs and from the hip (when using flutterkick)
5. from slow to sprint
6. recreational freediving
7. slow descent fast ascent
Too hard:
Imersion Esclapez black
Cressi Gara 3000
Cressi Gara 2000hf
Sporasub dessault plastic
C4 Falcon 30
all OMER plastics I've tried
Too soft:
Sporasub radical -it bend too near the toes
Good stiffness:
C4 Falcon 80 (model year -2000)
Cressi Gara2000, (but they have no angle so I don't like them)
If I should buy new blades from c4 I would go for the f25 or the f15, but try first.
Best of all for both of you is
1. Get your techniques filmed.
2. Fine tune it to the max with softer rubber fins
3. try every fin you can.
4. Buy the optimal fins
For me it took 5 years of mistakes and spent money on different fins to come to my conclusions. If I had worked with my technique very intensive in the beginning and then go for the fins I had minimized money and time.:waterwork
I hope this help you
And one important thing; the footpockets shall be tight to get the best performance. The footpockets fit can ruin a fins performance. Best is the footpockets that are fitted on monofins with open heel. For max performance choose fins with an open heel solution, the worst is that theese pockets lack in comfort.