I think the one hour PHYSICAL is a great idea for the following reasons:
* Body conditioning - help prevent tennis related injuries (e.g shoulder, back).
* Intervals will help improve your o2 capacity and hence your recovery between points when playing.
* Different forms of physical/cardio will improve your fitness overall and should help you be mentally prepared in your matches as well as maintain higher level concentration.
Just my thoughts!
Having gone through a hellish hot weather match last week, I would say adding an hour of tough physical training every week couldn't possibly be a bad thing. Match fitness was a major reason I lost.
I vote/agree physical conditioning.
Saw your vids, nice hitting, definitely seem to be at least 4.5+. I'm approximately in your same boat... play 7-8hrs a week, and I think physical conditioning has improved me considerably (more than adding another 2hrs of hitting). Not only does it get you fit for longer matches, but it enables you to work at high intensity during the few precious hours we have to practice.
From the few lessons I took from guys that played on tour, they stressed the importance of getting in shape to play tennis (tennis does not get you in shape past the 3.5 level).
In running terms... let's say you run an 8 mph pace for a 5k, playing tennis to get into shape is analagous to going out to every day and running an 8 mph pace 5k, and expecting to get faster at running.
For lower level players (eg. 3.5 or below), I can see adding an extra hour to hitting being more important, but at 4.5+, most folks strokes are already developed, just need to keep hitting at a higher intensity, and be able to sustain that for longer, and you need a high level of cardio to keep that up.
Alternative you could end every training day with sprints, and use the extra day of training for resistance training and/or stretching (eg. injury prevention).
my $0.02
edit: i was presuming you weren't in the best physical condition... i read that any murray runs 400s at 60s, and training i've done with some recently former D1 guys says, I need to run a mile under 6, and ideally closer to 5min (for my retriever style of game). Given these metrics, if you're already there, maybe another hitting day would be better or just focus on injury prevention.