How does the iGen3 print engine compare with docucolor technology?

Docucolors use generation 2 technology:
dev -> drums -> ITB transfer belt -> paper
registration is via hard edge

The iGEN3 uses generation 3 transfer technology (image-on-image development directly on the photoreceptor belt):
Dev (HSD) -> Galaxy belt -> paper
registration is on the fly w. CCD skew correction (IB/OB and Lead edge)

The iGEN can also handle up to 350gsm, while duplexing, with no reduction in speed!

Yeah, the computerized registration is incredible, I don't know what the iGEN's specs are, but the industry is moving towards a .5mm accuracy.

It's kind of like the difference between "race track" duplexing and duplexing trays, you will be asking yourself "Why the #$%@ didn't that happen sooner?"

I heard that igen speed varies according to media weight (under 100 and over 300 gsm I think) is this true?

No, that is the exact opposite of what happens. It's one of the big selling points of the iGen is that it doesn't slow down.

I just talked to a Xerox tech, he says the media handling capabilities like to break down, good thing it's on a service contract.

from experience with regards to the speed issue we run stocks from 100gsm to 350gsm and theres a massive speed difference between to 2. we can run 1300 sheets approx of 100gsm an hour duplex and then only print 800 sheets approx of 350gsm. then also there a speed issue with black only mode if you have the NVMs the black only mode will self adjust to refresh the devs to stop the toner age dropping to low

The Igen has to allow more time in the Fuser for heavier stock, but it is not the same speed difference as with the Docucolor machines. You can change the Auto Toner Purge in the NVM's to minimum adjustments when running in Black Only Mode (see 'GP 8: Adjust Auto Toner Purge Setpoint' in your CMM).
The fuser can also slow things down if you are running two different weights together, like heavy cover stock and text weight, because the fuser temp has to keep adjusting up and down. When running slip sheets in a job we always set the GSM to match the job stock to avoid this.
What effects how many pages per minute on the Igen is primarily the size of stock - smaller stock is faster because more pages can be imaged on the PR Belt, so less rotations are needed, etc.

We have an igen3,

Printing on 300gsm Auto duplex gives us around 1600 sheets of SRA3 per hour.
When we run 100gsm, it goes up a fair bit.

Neil