The T5's standard suspension parts are the same as the
GLT. But the T5 comes with 16 inch wheels and wider
tires. (I have a S70 98 T5M.) You can get a sport
suspension with the T5 but many say it is too stiff.
I'm not that familier with the R models but they are
visibly lower and I assume they have different springs
and shocks.

You do have to be careful if you are adverse to getting
a ride that is too harsh. My wife has a 95 855 GLt wagon.
It is stiffer then my 98 and lower. It corners well but
has a very harsh ride (Volvo softened things up with the
S series). My T5 with Bridgestone Potenza tires will still
out corner the GLT (T5 is also lighter) and still gives a
much nicer ride.

So, I would look at stiffer roll bars and possibly some tires.
You can often find the 16 inch wheels off the T5s at a good
price (try eBay or www.ipdusa.com's classified section). If
you want to go shocks I'd look at after-market since the OEM
ones probably are expensive and won't offer much difference
over what you have now.