Getting a metallic, trebly tone?
 

I want a tone that is clangy and metallic, yet still clear and punchy, sort of like a Gibson G3 or a high-output P Bass. What are the key factors in achieving that sound?

Steel strings.

First and foremost, new, stainless steel, roundwound strings. Second, don't eliminate the bass from your tone. Otherwise it won't sound like a bass. Third, experiment with where you play on the bass itself - most likely from the bridge to about half way between the bridge and the neck will give you the tone you're after. Then, add effects/outboard preamps, etc. But start with new strings.

low action on your bass, nickel roundwounds, boost treble on either your bass or amp. Also, running direct often lends itself to clank.

Try D'Addarrio Pro Steels. They are affordable and very very bright! I did not see if you are trying to get this live or in the studio. If it's for live, use a cab with a tweeter in it. If you don't have a cab with a horn in it, work with the EQ on your amp. Add frequencies 4K, 1.6K, scoop 600hz, put some boost in the low end where it is punchy and not muddy for your rig. You also did not say if you have an active bass which might help.

Equalizer. Pick near the bridge. Ss rounds. Ibanez atk.

P-bass, Stainless Steel Round Wounds, stiff pick near bridge, powerful amp (~500+ watts into 4 ohms), good cabinet(s) with 410s or more and a horn/tweeter. Pound it. Wear ear protection.

+1

exactly what I am doing and it gives such a clear and cut-through-the-mix sound.
Squier MF Sig, Hartke Lh500 amp, Fender Rumble 410 cab, Rotosound 66s

my bandmates love the sound and so do i
If ya want some clanky but still hold true to a bass sound that is a great setup

High mids will give it that really clanky sound.

My sound changed dramatically when I went to biamping. Having 15's for the low frequencies and 12's for highs with an active crossover made it possible to layer crisp high end over a fat bottom end. Out of everything I've done, it's made the biggest difference in sound, giving me a combination Tool and Entwhistle vibe which is exactly what I'm after. Biamping is a financial consideration, because you need a suitable preamp, stereo power amp or two amps, and probably separate cabinets, but IMHO it may be the best way to get the sound you're after. I play Ernie Ball nickel steel roundwounds, use a pick, and have my Yamaha BX-1 humbuckers on the "parallel" setting, which gives a more trebly sound but still has plenty of punch. I'm pretty sure that it's a "parallel/series" switch; don't yell at me if I'm incorrect! I also recently got a DOD stereo graphic EQ so now I'm separately equalizing high and low frequencies, which is a bonus. My goal sound-wise is to have chunky ringing highs with teeth-rattling lows, and I'm pretty much there but always experimenting. I'm planning on trying Ernie Ball stainless steel strings soon, and am in the process of making some stainless picks in different gauges to see if they give an even better attack than celluloid ones. You're after a pretty cool goal, EXILE03, and good luck!

P-bass...Steel Strings, tone knob cranked. A la 90s punk!

^^THIS^^
Pro Steels are extremely bright and trebley. Love 'em!

I played a Stingray with brand new rounds on it last week.
Easily the most metallic sounding bass I'd ever played.
Wasn't a fan since that's not my style, but it was all the guy had in his studio that wasn't a 5 or smashed.