4th gen was just lighter... slalom on the 4th gen is a few ticks behind and skid numbers are fairly close depending on the sources. The biggest hit against the 4th gen was a rough skidpad.... on smooth skids it did really well but on a rough surface the rear would slide out if upset.
4th gen 1LE cars posted .90~.95 (depending on the year/tire options/etc)
4th gen Z28/SS cars posted .86~.88
5th gen V8 cars post .88~.90 (if I missed some higher results please correct me)
Overall it's fairly close on the 'numbers' but in the slalom there is a ~3+mph difference..which shows the 5th gen is really composed in quick transistions versus the 4th gen.
Of course if you change the stock tires off a 4th gen in favor of better rubber it throws the entire comparison out the window... tires make or break these tests.... toss the factory RSAs (245/50R16s) for stickier/wider rubber (the 2010 is packing 275/40ZR20 Pirelli P Zeros for example) and you would increase the numbers for these test. So if you're 4th gen had a tire upgrade that might explain why you would come to that conclusion.
2001 Camaro Z28 M6 (MTI Lid/FRA, LS6 Cam, BBK LTs)