Not sure if there's more armour knocking around, there is more health though in the subway, just past the turnstiles IIRC, and again near the end.
Just take your time, use lots of cover, & maybe throw some grenades too.
If you've got to the subway, you're nearly there.
Couple of guys down the first corridor, at the end on the right. Then you come down to near the turnstiles etc. Keep in cover, maybe chuck some grenades. Waste them with the carbine. More come up the stairs, waste them too. Watch out for people hiding behind pillars & turnstiles. Off down the stairs, to the platform.
Once you get down to the platform, take cover behind the pillars & shoot as many cops as you can, loads of them will pile down the stairs over the tracks on the opposite platform. Once the brothers start off down the track, run after them. They'll stop at one point to shoot back at the cops again, so join in with them, then head off again when they do. Stay in the middle of the tracks, & watch out for subway trains! (I got run over on one attempt). You'll soon get to a hatch, & some stairs leading up & out. IIRC, there's more health or something in a room near the bottom of the stairs. Once you've left, there's a handy SUV for you to jack, then you need to get the hell out of there & lose your 3 star wanted level (I kind of cheated by just phoning Kiki).
---------- Post added at 22:22 ---------- Previous post was at 22:20 ----------
I killed Packie one time with a grenade
Each time I attempted it, there was always a four door SUV thing by the exit.
As for the wanted level at the end, I phoned Kiki, lol. Almost did it one time without phoning her, & just by driving & evading, but my car blew up.
---------- Post added at 22:24 ---------- Previous post was at 22:22 ----------
IGN guide:
http://uk.guides.ign.com/guides/827005/page_113.html