Mystery
problem where 25fps videos played at 60hz play 4% faster
I don't know such problem. Please give me a link to explanation of the problem.
each have a processing cost
You are mistaken. ReClock can do SVP work lighter. For example:
SVP without ReClock: 25 * (12:5) = 60. Only 1 of 5 source frames showed so in 1 second you see 5 source frames and 55 calculated.
SVP with ReClock 4% slowdown: 25 * (5:2) = 62.5 -slowdown-> 60. Only 1 of 2 source frames showed so in 1 second after slowdown you see 12 source frames and 48 calculated.
With ReClock video quality is better because it consists of more source frames and less calculated frames. Moreover SVP needs to calculate less new frames. GPU load is less. Moreover-2 after slowdown you get 24 fps source speed instead of 25 fps. It gives less calculation of motion vectors by 4% every second. CPU load is less by 4%. 
In any time you can enable or disable ReClock and allow any speedup or slowdown (up to 10%) to get more video quality (and less CPU & GPU load).
Reclock... also costs on image quality
I can't confirm that. ReClock don't touch video frames. It make changes to audio track only.
So, what is bad with ReClock and 25 fps video?
