The Rs had a bigger turbo and ran more boost. Max boost was limited
to something like 10 or 30 seconds then it backs off to the same
setting as the non-R turbo (not that in 10 seconds you would be
pushing 80MPH from a stop). All tubros limit boost in
first gear if you have an automatic transmission. Actually,
the word limit should probably be "manage" since the ECU in
modern cars allow the designers to exploit the full power and
still keep the tranny parts intact.

Volvo has never supplied a LSD on any cars in U.S. market.

In Europe, the Rs (at least the 70 series Rs) had a viscous
coupled transmission setup (manual tranny, I assume) to improve
traction. The 70 series R models never made it to the U.S.

I think there is an after-market source for LSD but it would be way
expensive. I'd imagine LSD would also add to the torque steer.