I can't see the difference between ProRes 422 and ProRes Proxy from HDV

When I watch a video in ProRes 422 and ProRes Proxy formats with Quicktime, I just can't tell the difference. I stop them both on the same frame, blow them up–and I can't tell which is which. I am filming with a Canon XH A1 to HDV tapes in 1080i. I produce documentaries for television broadcast. Until last year, I set FCP7 to capture and edit in HDV. I switched to ProRes 422 because I assumed there would be a big improvement. But all I notice is that I'm filling up my external drives very quickly.

So if HDV is recorded at 25Mbps, then is it overkill to capture with ProRes 422 which is 126Mbps. Can't I just capture with ProRes Proxy? At 38Mbps, Proxy is still more Mbps than the video was recorded with. Theoretically isn't it all going to look the same?

I appreciate your responses.