There are a few things to think about here.

For one deployed gear basically acts as a speed break, many new GA planes are working to allow gear extension at full cruise so the gear can double as a speed break, notable Diamond has done this on their new twin, and talks about it in a few of the videos. So from that stand point they act like any other drag creating air break.

Now lets talk about air flow over the wing. While a wing generates lift as a whole item, the lift is distributed along the length of the wing as is the air flow. Most GA planes (and the war birds you have pictured) have the gear in a more inboard position. Deployed gear may create a bit of turbulent flow on the inner part of the wing but the rest of the wing still generates lift while the gear is down and interrupting air flow, possibly effecting lift.

As for speeds you have Vs0 which is your stall speed in landing configuration which could differ from your Vs but should be confirmed in your POH for each aircraft. I would think from a design stand point the engineers make sure that the wing generates enough lift for take off and landing and safe flight with the gear down but focus mainly on aerodynamics from a gear up perspective as that is the common setup of a plane. You should also note that the drag from the gear will affect climb performance so you will want to get that gear up quickly once you are flying.

There are a few things to think about here.

For one deployed gear basically acts as a speed brake, many new GA planes are working to allow gear extension at full cruise so the gear can double as a speed brake, notable Diamond has done this on their new twin, and talks about it in a few of the videos. So from that stand point they act like any other drag creating air break.

Now lets talk about air flow over the wing. While a wing generates lift as a whole item, the lift is distributed along the length of the wing as is the air flow. Most GA planes (and the war birds you have pictured) have the gear in a more inboard position. Deployed gear may create a bit of turbulent flow on the inner part of the wing but the rest of the wing still generates lift while the gear is down and interrupting air flow, possibly effecting lift.

As for speeds you have Vs0 which is your stall speed in landing configuration which could differ from your Vs but should be confirmed in your POH for each aircraft. I would think from a design stand point the engineers make sure that the wing generates enough lift for take off and landing and safe flight with the gear down but focus mainly on aerodynamics from a gear up perspective as that is the common setup of a plane. You should also note that the drag from the gear will affect climb performance so you will want to get that gear up quickly once you are flying.