I have listened to OB1 and IB1 but have not tried the new "i" series. Having talked to the PMC dealer, the "i" series does offer a bit of improvement to the old series in terms of refinement but the changes will not be day and night. I don't think there are many people who own the "i" series yet so I don't know if they prefer these more than the older version. It is best that you can listen to them personally. Frankly speaking, I won't expect huge improvements going up to the "i" series with the new Sonolex tweeter and designed bass driver. If one is looking for a punchy sound, deeper bass with greater presence, larger speakers with bigger drivers will be necessary for a big change. I know because I have demoed the LB1 "Classic" and the new improved LB1 Signature(with upgrades in crossover and parts) side by side -the sonic differences between the two are very subtle to the point of negligible.
The OB1 is 2X heavier than the GB1 by the way so you can imagine the "weight" of the sound the former will have in comparison to the latter.