This could start arguments!! In my opinion the 5000's sound slightly better at "normal" volumes but the pentas will sound better as the volume goes up and will of course go louder. But the 5000 looks a lot more stylish. Why the panel speakers didnt sell well when new is a mystery to me.
Speakers should be listened to first though because what I might think sounds good, you may hate.
Also if its just the sound you are worried about and not the appearence, dont discount the uniphase range as some of the larger uniphase speakers really are terrific and can be bought a lot cheaper than a pair of beovox panels.