well what opamps are you using? have you ventured outside of of the stock rolling kit?
the p4 vs the sr71b single ended vs single ended, In my opinion using the 2 Single LME49990 in L&R 2 HA5002 Buffers 1 Dummy Buffer in the ground and 1 LME49990 in Virtual ground in the p4, to me the p4 sound is superior to the SR71-B.
i have owned a good ammount of amps and i havent found a amp that the P4 using the right opamp configuration couldnt replicate as good or better in sound quality.
the p4 is powerful, allows you to change the configurations of biffers and opamps thus giving tyou the ability to change the sound signature.
i cant exactly say which opamps and buffers would get you that ''sound'' you are looking for, but i totally believe you could achieve the sound with the p4
you might want to talk to Hiflight on here, he makes complete kits for the p4 he can pretty much throw any buffer/opamp combo together, he can also put together a kit that will give you that sound your looking for.
do nore that rolling opamps and buffers may take some time to get it just right if you are looking for one particular sound in general.
obviously one think to take into consideration is with opamp rolling it allows you to not be stuck with just one sound with just one signature from a amp. where as when you buy say a 700.00 amp after burn in what it sounds like is what it sounds like, the only way to change that is to change the amp completely to another amp. where as with the p4 dont like the signature change the opamp and now you pretty much have a new amp.