I've tried the SEL Lorenz PCC88's and i have to say i prefer the sound of the Siemens over those, but not tried any E88CC Lorenz tubes yet.
I wouldn't say the Siemens have massive bass impact, more like a subtle warmth, but the 650's are a warm can anyway, so can probably get away with a less bassy tube.
I don't know how to describe mids other than recessed or not, but vocals sound superb on the Siemens as far as i can tell.
Treble is smooth and airy, not bright at all, but aren't the 650's a bit veiled in the high's? could do with some sparkle from what i've read on them.
Soundstage is expansive, more so than any other tube i've got.
Don't know if all that helps any.