Theodoros,
You are welcome, glad you found it useful.
I don't know where you live, but basing this on the USA for now, on the B&H website there is $1000 difference between the P7000 and the P5000, so I would consider that non-trivial and worthwhile spending only if you need a 24 inch printer. The P7000 is also a very much larger machine, so depending on your space, size may be a consideration.
Right now the P800 is $900 (after rebate) plus $200 for the optional roll feeder, so $500 less than the P5000 after its rebate. For the difference of $500, the P5000 gives you ten inks instead of 8, a built-in automatic mechanism governing the movement of the roll feed, internal roll paper cutter, a larger print-head with higher print speed, a more refined printhead cleaning mechanism (can clean in pairs of colours rather than the whole head only), the economies of much larger ink tanks in terms of cost per ml of ink, and finally an apparently more robust build quality because the P5000 is designed for production, while the P800 is designed for more casual usage. If these additional features of the P5000 matter to you, the $500 price difference would seem to be well worth it.
The bottom line of course, apart from any budget constraint, is to buy the feature set you need or prefer.