Do you want to show what your typical render settings are, please?   I take it that you are using Firefly in both.   It should work the same way in both. 

But, another thing:  I've never had a problem (of that sort) with 7, but 6 was hopeless, to begin with.   It came with an instruction to check for hardware drivers - so I did.   Nothing was found, but Poser 6 couldn't render anything for me.   Just before launching a home-made ICBM towards Curious Labs (as they were), I ran a new check for drivers.   That time, there were new drivers and they fixed the problem.

You shouldn't have to re-install Poser to fix anything.   I know it's a common recommendation around here, but it's like saying, "Dirty windows?    You need a new house!"

I found P6 faster than P5 and P7 about the same as P6.  

Do your P7 renders complete very slowly, or do they bomb out?