Big 4 of 2012 or so > Big 4 of 05
Yet in saying that the big 4 of 05 would tear everyone apart as of this year and I'd be tempted to say 2013 as well.
In January Hewitt, Safin, Roddick and Fed looked lethal, and all played beautiful tennis.
If they were to go up against the Big 4 now? Djokovic is the only one who'd consistently bag wins outside of Rafa on clay.
Murray back from injury and still not 100%, Fed is practically a complete shadow of himself barring his serve and can barely hit a BH winner, Nadal can't play on grass and Djokovic still seems to be consistent at not actually winning majors but getting to the business stages. 1 major win in 2 years now yet all of them he's made SFs barring Stan?
If you threw them in a Hardcourt RR tomorrow 05 would probably win handily.
Then we reach the rest of the top 10.
Nalbandian, Davydenko, Haas, Nadal, Gonzalez, Coria
vs
Wawrinka, Raonic, Dimitrov, Nishikori, Ferrer, Berdych
Barring Wawrinka do you see any of these guys consistently beating those above? Even then being the headcase Wawrinka can be it'd be interesting to see how good he would go.
The argument repeats itself
Fed Nadal and Djoko > Hewitt, Safin, Roddick at their peaks
05 Fed > Current Nadal and Djoko
YET
The Top 20 of the 03-07 era would slaughter the Top 20 we have now.