[The Scientist (OP)]

Same in substance? Same in quality? What do you think? Thanks!

[BenV]

Same substance, but the fibres get shorter with each recycling round.  Paper that has been recyled a lot goes into tissues and toilet paper, I believe.

This also will mean less clay (used as a brightener & smoothener in expensive new paper), and the recycled stuff will probably have more optical brightners added to make it white again.

[Mazurka]

Didn't you do a kitchen science about this Ben?

I understand that a paper fibre can be recycled on average 6 times before it has become too short to be useful.

It is the same substance, although as with "virgin fibre only" paper it comes in different grades and qualities. Paper process waste (i.e. that has not left the paper mill) is often "recycled" into virgin paper. 

As an aside, the recycling of paper raises some very interesting environmental issues.  This primiarily relate to the environmental cost of transport. 
Is it better to haul paper in 30 Tonne loads  from Cumbria to Kent (Aylesford Newsprint produces around 1% of recycled newspaper globally and recycles a significant percentage of UK paper waste) on the back of a lorry
-or-
Dispose of the paper to landfill where the landfill gas is captured and used to generate electricity?