I've owned two Bassdrives and the Turbo Rat is my pick there. They're very different pedals, though. The Turbo Rat will do less distorted sounds, but they're more edgy and less warm and having less gain will also cause the pedal to lose bass. At the gain setting I use, the bass response actually seems pretty equal to my clean signal, which is pretty impressive, given it's tight and heavily distorted sound. I'm glad somebody thinks it sounds pleasant because my brother (guitar player) complains about my harsh assrock he calls it sound. I also run the Turbo Rat with my Xotic X Blender, which gives me in effect two channels, one with the blend which is a warmer, more overdrive like sound (though still feels pretty gainy), and then full on which is what you hear in the samples. For these samples I'm using a Fender American Deluxe Jazz bass with Seymour Duncan Quarter Pounders (passive), both pickups full on. And for reference I used my SVT-3 Pro instead of the V4BH I used for my other distortion pedal samples I've posted on the forum, though the difference in amps isn't a big deal as far as these samples are concerned.
I haven't heard of any Turbo Rat mods, but I can tell you it sounds pretty tight with a clean blend. A lot of distortion pedals sound a little flabby on my low E string. I have to play strings lighter than mediums; heavier strings have more string tension, and if I play mediums I break them all the time at the string core because I play so hard, lighter strings with less tension I don't break as often. Plus my main gig is with a band that tunes down a half step. So it's cool that the Turbo Rat stays tight on my low E string, and with the clean blend. I recommend the Xotic X Blender because sometimes, depending on the settings and the distortion pedal, the bass knob comes in handy to give a little more bottom to the effected signal. I also have some distortion pedals, like the EBS Multidrive, that have too much bass, so in the Xotic loop with a little bass cut sounds MINT. If I get a chance I'll do some Multidrive samples too.