DRU-510A says 4x but actual is 2x!

Hi,
Had a Sony DRU-500A and all was Ok with Nero.
Got a DRU-510A and can now record with Nero at 4x on DVD-RW.

Abboying problem is with DVD-R it says my ritek discs are OK for 4x but takes 1/2 an hour! so is running at 2x

What is going on?
Cheers.

Mate, cross posting is not cool. One will do