Right first things first (speaking from experience here) pitstops conversion looks the poodles plumbs but as they have always said they will not realise a product/service until they are happy with it themselves.
The only other place that does the conversion kit is aw tracksport, this is where mine was from. are you just going to have the eaton as a g40 charger replacement or are you going for big power??
Either way an eaton on it's standard pulley will create the same (if not a tad more) boost as a g40 full blend on toothed belts. However you will loose some low down torque as the eaton creates more of a linear boost increase whereas the g40 would come on boost hard from 2.5k rpm.
you can obviosly fit a smaller pulley to the eaton to get it to spin up a lot earlier but this still will not overcome the loss of low down torque a g40 produces. That said after about 4k rpm the eaton is a totally different beast!!
prices to be aware of:
£550 for the conversion kit
£100 for the pullies
£400 for the mahosive front mount intercooler (a must!!)
£100-150 for the eaton
£250 for a custom remap
£110 for green injectors (really would recommend these if you haven't got them already)
AW are offering fitment of the kit for £100 which is a bargain to be honest, i know what i'm doing but if you aren't really clued up and don't like cutting bits from your car (for clearance reasons!) i would really consider this option, it took me at least 8 hours to do mine but know i now how it's achieved i could do it in 3-4 hours i reckon
£1550+ £100 fitting is what it would cost to do it all properly, i would suggetst a compression test before any of this is carried out as wacking a load of boost onto a tired engine will kill it!!
My car is running a 15% smaller pulley and is making 20-22 psi boost on a standard bottom end, head, cam and exhaust manifold. During the remap which had to be aborted (due to the forge motorsport pulley slipping on the eatons shaft and intercooler end tank failure) we worked out that my G60 injectors are working at 80% duty cycle, that's 5% away from being static which isn't good!!
My car is buring enough fuel for 185-190 bhp!! They gained a couple of car lengths on a prsche 996 carrera while doing a full load test from 2k rpm onward in 5th up to 7k rpm which is a true 140mph, unlike my speedo reading which is well out due to my stupidly small tyres (195/45/13's
))
So the long and short of it is, unless you are going for big power i would stay with the G40 charger, if not then the eaton is definately the way to go
Would a chargecooler a la Jabba be a sufficient replacement? I like the potential here, I like it a lot 
Makes me wonder if I should just get a mk2 or 3 shell to put it in though and put my GT in the mk1 