It is stupid to go with anything less than 1.9'* IMO. With 1.9'* the valves open faster and more than with any other size. They don't hurt idle quality any noticable amount, they don't cost any more, and your gas mileage with normal driving will actually increase. Why people go with 1.8'* I'm not quite sure, but they are the same thing but with only 2/3 the gain. The only advantage I can see is it would be easier to get away with using stock springs with them.
ZZP'* rockers only go up to 1.8 because thats all the more they have made so far. When tehy were released (not too long ago) they were only available in 1.7'* (for people with smaller cams like VS, Stage 1, S1X, etc..., but since they have added the 1.6 (for people wanting the roller tip with their cams but don't want more lift) and 1.8 ratios, and I'm sure 1.9'* will soon follow, they just haven't been released yet.
I-Win rockers are modified stock rockers and reliability is great...they are the same as whats in the car stock so I don't see how they could be unreliable. People don't complain about the quality of stock rockers. All they are is stock rockers with the pushrod hole relocated farther out from the center to raise the lift. They are the same as the old ZZP rockers, which is what we had on the GTP, and being the quickest and most powerful stock cam car they obviously worked pretty good. When we took them out they still looked like new (they only had 15k miles on them though) and we threw them in the Monte and it performs great, it went from 9 to 2kr with the rockers, 41-919 plugs, and a 180 t-stat. We also have them in the SSEi and have for 70k and they are still perfectly fine. They killed all of the 7kr it had when we installed them. I definately think they are awesome rockers, and being cheaper than any of the others I can't see how you could lose! They are definately what I recommend!
Although it isn't required, I highly recommend the use of stronger valve springs with higher ratio rockers. We put the ZZP 1.91'* in the GTP with OR pushrods but stock springs and at 15k miles it got valve float at around 6k or so and higher. So we put in what at the time was ZZP'* 85lb. valvesprings and no more float. However, we put the I-win 1.9'* in the SSEi with 70k on it, and now even with 140k on it, it will rev to the 6200rpm limiter smoothly with no problems, no float at all even with the stock pushrods. So you never know if you're gonna get valve float, but its a good idea to get the stronger springs just so you don't have to worry about the possibility of yours breaking.
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!