IDL alone is worth the upgrade to 8/PPro2010. Previews are not as nice as P7 because of new lighting tech. Although, it's easy to make a "correct" click-on lightset to work with before using the "real" render lightset.. Too fussy for me but,,,

P7 was my least favorite upgrade. P6sr3 was very stable. P5-P7 will only give you black shadows. PPro 2010, though counterintuitive for me, produces the best quality renders I've ever made in Poser. IDL being the real star and it is stable.  Watch for sales. I'd skip P7, P8