regarding the ability of the steel wheels being able to take 80 psi that has been addressed repeatedly on this forum .
there are a bunch of misinformed posters who believe that these wheels will not allow 80 psi .
that myth has been debunked at length by the most knowledgable tire guys on this forum such as capri racer , fast eagle , and others .
the original steel wheels will take 80 psi with ease .
regarding upgrading your tires it is more important to increase the load rating of your tire no matter which way you do it .
Load Range and tire size are far more important than brand .
So if you gan go from a "C " rated into a "D" or an "E" that is a good way to go.
If you can go to a 215 or 225 section width over your stock 205 that is another way to go .
the important number assuming you are only considering ST tires is the weight capacity in pounds your replacement tire is .
there are plenty of choices in 225/75 R 15 in load range C and in load range D .
in practical experience the advantage of a 225 over a 205 outweighs any issues with rim width .
the best solution I have seen in 15 inch tires is the Continental Vanco 2 tire.
http://www.tirerack.com/tires/tires.jsp?tireMake=Continental&tireModel=Vanco+2&sidewall=Blackwall&partnum=27R5V2&tab=Specs
size 225/70R15 C has a load rating of 2470 pounds on an LT tire scale. This is also a tire that is rated for 99 mph unlike an ST tire at 65 mph rating .
it is also available in a 215 section width , also with high load ratings.