Where's Pur? unless maybe an abreviation for Perpinon?
If there are just 2 of you and both drivers then I'm guessing you just want to "get there".. rather than admire the 'scenery' along the way?
I did Calais to Barcelona (to rescue relatives from the ash cloud debacle), used the tolls as I wasn't hanging about and it took me 7am till 10.30pm, and from that 15.5hours, 12.5 hours was actual driving. 882 miles so average speed was just over 70mph (you've no chance of that if you avoid tolls as it's a much tougher drive).
Barcelona to Murcia can add on another 360 miles or so over say a further 6 hours, so in total your looking at around 20 hours of actual driving. Personally I'd forget having one drive and the other "sleep" as it doesn't work (safely or effectively) in practice. Better you both swap every couple of hours or so, keep each other company, take regular but short breaks. I stopped for around 10mins each and every hour, hence broke the trip up into loads of small chunks (which kept me mentally fresh 'most' of the time).
Consider you'll be leaving Calais 7am-ish but you wont want to be up that early second day, hence you'd be wiser to try and do the bulk of driving on first day. You've around 1250 miles so if you stop at Perpinon your ratio will be about 755 (12hrs) vs 495 (8hrs). If you get to Barcelona it'll be around 880 (14hrs) vs 370 (6hrs)
As others have said use www.viamichelin.com, I printed out these 3 stages as separate docs..
Calais to Lyon, 475 miles, allow 8 hours
Lyon to Perpinon, 280 miles, allow 4.5 hours
Perpinon to Barcelona, 120 miles, allow 2.5 hours
and then you'll need..
Barcelona to Murcia, 360 miles, allow 6 hours
If/when heading back the other way, again I would aim to do the bulk on day1 so stop at either Lyon, or better still Dijon (nice place).
Drive safely! ;O)