The 1.9 ratio are going to give you more lift, whereas the aluminum ones give you less lift but generate less friction because they are full roller rocker arms. INTENSE used to make full roller 1.9 rocker arms but had many problems with them. The SLP 1.8'* haven't been out too long, so the same problems may arise in the future. The 1.9'* are the stock rocker arms re-worked, so basically it is of OEM quality so you know you aren't hurting your reliability over the stock ones because they are basically the same.
Personally it seems that the 1.9 would be much better than the 1.8'* because of the fact that they have MUCH MORE lift. The 1.9 rockers have .4902 lift, whereas the 1.8'* only have .4644. Stock is .4128, so you can see it is a HUGE difference. I would recommend the 1.9'*, our GTP is the second fastest stock cammed GTP out there and it has 1.9 rockers, and so does the only one that is faster than it, basically because the larger rockers are like having a larger cam.
Hope this helps.
Oh yeah, 1 more thing, unless you plan on doing headers along with the rockers the 3.25 pulley you have is probably too small for your mods, and your car would mostlikely be faster with a 3.4 pulley.
1990 Maroon Grand Prix STE McLaren 3.1 Intercooled Turbo, 14.695 @ 94.49 on 12psi before cam/heads/etc.
1990 Bright Red Grand Prix McLaren 3.1 Intercooled Turbo, 14.819 @ 92.72, 189whp
1999 Grand Prix GT 9.75:1|K&N|160 tstat|No Ubend/Cat/Res|UD Pulleys|Ported M90/TB/Heads|XPZ|2.55"|Pacesetters|Stage 2 I/C. 12.442 @ 112.78
2000 Blue Bonneville SSEi Supercharged Gutted Airbox|K&N|3.4"|1.9'*|WP Pulley|Custom DHP|180*stat|41932'*|No Cat. 14.681 @ 94.80
2002 Dark Cherry Grand Prix GTP Supercharged & Intercooled
12.084 @ 114.38 w/1.743 60', 315.6whp, Fastest Stock Cam M90 GTP!
NOW XP CAMMED, 340.6whp with XP, stock heads, Gen 3 M90, 11.984 @ 115.84 w/1.750 60'!
Most HP Stock Heads Gen 3 M90 GTP!
2004 Red Monte SS Supercharged K&N|3.4 Pulley|1.9'*|180*stat|41919 plugs|3" dp|No cat/ubend|DHP|Shift Kit. 14.2 @ 98
GOT BOOST??? Friends dont let friends drive stock!