XP mode recording. Worth it???? what about SP????

Hey i just got my new JVC DR-m100s and am starting to record shows. I noticed that when i set the recording for XP, it gives my dvd of the show i recorded a Bitrate of 10mb. When i captured the same show to my computer(via firewire, so it was a 1:1 copy of the show), the bitrate was only 7.5mb.
Well my question is, if all the shows on cable are only 7.5mb originally, then it cant get any better at 10mb, can it? and if so, then is it even worth recording in XP mode(are there other benefits other than bitrate?).

another thing im alil confused on is the FP mode this JVC has. It lets you set the amount of minutes you want(ex. 134 minutes) for a dvd recording. What im confused about is what would be the quality if i set a dvd recording at 1 hour and 30 minutes. That would be between XP and SP, now what would the quality be closer to?

IF i set the FP mode to 45 minutes, will it be better than XP quality?