Thank you for posting your question,The locality of the bathroom in comparison to the kitchen doesnt affect the IP rating of the downlights required for the kitchen. I would however suggest for any downlights you use fire rated ones, which have a dome which fits in the ceiling void, and example can be found here.
The requirement for bathroom lights is dependent on where you place the lights within the bathroom, I understand none will be above any bath shower or bath which means they wont be in zone 0 or 1, but may be in zone 2 which would require IP44 as a minimum. The document here gives you a diagram showing you how the bathroom IEE zones are defined and from there you can determine if where you plan to put the lights will be outside of zone 2 at which point you could use a IP20 rated down light, however I would suggest you use IP44 for the bathroom.
Please let me know if you require anything clarified.
IP65 are unlikely to have a significant benefit in the event of the bathroom flooding, since the water is coming from the void above the light not below it which is how most are rated\tested. It wont harm having a higher IP rating, however by in large the amount of junction boxes you will have in the void and ceiling roses etc you will find its likely to trip the electrics \ give rise to electric regardless of you selecting IP65 or IP44 for the kitchen.