I have the Roddio i-10, so I'm glad your favourite is the i-8. I haven't gamed mine yet (weather is pants), but I've had 1 range session with the PW and 7i.
I've gamed Quadra 100i in 'S' flex so I can give a quick comparison. The Roddio in 'SX' flex feels heavier and stiffer. Quadra was longer, easily. PW in Roddio hiting about 130yds. I think the Quadra was about 140 - 145yds. It seemed to hang in the air forever. I had Yamaha Tour in the Quadra and Srixon Pro 100 in the Roddio. The Yamaha PW was 46* and the Srixon is 48*, so this definitely had something to do with the extra distance, but the Quadra seemed to kick more with a softer feel. Whether the Quadra is softer feeling has to do with the s20 steel of the Yamaha or not I don't know. With the 7i I think the Roddio is lower, something I definitely wanted to see. I think they're lower than Modus 3 too. No noticable difference in height in the PW. The Quadra went left more so than the Roddio, possibly due to the weaker flex. My fitter said the Quadra CPM'd out at 'R' flex!!
I would love to try the Quadra in the 'Pro' flex, as I think they would be a better comparison flex-wise, but overall I would recommend you try the Quadra shafts, for the feel if nothing else :)
In an ideal world I'd have the ballflight and control of the Roddio with the feel and kick of the Quadra. They both look great :)