I just wanted to post about the E4JS as it doesn't get many mentions and after a few meetings, I've got it going really well.

My setup is for medium grip carpet on Sorex 28JB rubber tyres in 17.5 boosted Stock class..
Additive: Jack the Gripper, full rear coverage, almost full front coverage bar a rim on the outside, about 15-20mins before.
Ride height f/r: 5mm
Downstops f/r: 3
Shock position f: outermost hole on tower
Shock position r: innermost but one on tower
Antiroll bar on front only, the stock one from the RS
Shock oil: 40wt allround
Springs: Stock
Camber & Toe: not checked lately but looks 1 degree
Diff f/r (didn't get on with the spool, an acquired taste)
Steering on transmitter: full front lock, no D/R reduction (I find makes for an agile car)

Was comparable in pace to Mi4s and XRays, albeit, like me, in the hands of relatively inexperienced drivers.

Handling was agile, lots of sidebite, so much so there was some bodyshell rubbing on the carpet. Might put the stock rollbar in the rear and a heavier one up front.
Stiffer springs also a good idea - I have some Yokomo and Schumacher ones to try.

If I was going to upgrade the car, I'd look at steering assemblies with less flex/slop first.
Durability is excellent, has shrugged off a few heavy impacts, though a freak accident (Mi4 embedded in the side of the car) slightly damaged a side pulley (still works) and flipped the belt over.

If anyone is thinking of doing a chassis for the E4 series, one that uses the JS front and rear sub-chassis would be worth consideration.