Agree with Brian, by watching prices the 7 can be generally the bargain of the group, big bright finder and auto parallax corrected lines for 35, 50, 85-100 and 135.
According to Dechert's book seems the finder was SUBSTANTIALLY improved (brighter, clearer, easier to adjust) on the second batch of the 7s model, usually called 7sZ, but alas they are scarce and command higher prices.
The P on the other hand is a really elegant camera with reflected lines for 35, 50 and 100, all them always visible in the finder. I'm waiting for one to ship from the US so probably I'll be able to tell more about it soon
Meanwhile, I'm sure our own P-man (that's Joe) will come to the rescue and explain you the excellences of that camera
As for the lenses, common agreement is that the 50/1.8 in each of its incarnations is a great optic. On 35mm, the prize seems to be for the later black 35/2, even though the 35/1.8 gets some exceptional feedback but somehow seems to go a bit ignored (which means you can get it for a better price

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A good non-Canon option may be the excellent tiny CV 35/2.5 lens.
PS: forgot to add, the 7 had so many features by its time that they didn't remember to add the 'down to world' accessory shoe
