I had a pre-Peavey SD80 and it had plenty of gain for me. Did it have 5150 levels of gain? No. More gain than a stock JCM800 with more of a lower mid push like a Bogner.
I don't think the Peavey ones should sound any different (for the clips I heard). The differences I heard were slight and could be chalked up to different amps, tubes, etc. and nothing to do with pre or post Peavey production.