There are loads of ifs and maybes on the ride, if you wish to take a path that's not on either of the files distributed, that is your choice The points are a couple of differences between routesheet and GPS, both have been the "official route" at some time in the past, you've paid your money, you can take your own prefered route .............
Out of interest, I've looked at files sent to cyclists, and I'm a bit confused. I'm fully aware that the route sheet follows the A44 through Worcester - it was following comments from past tandem outfits expressing a dismay at the cycle route option. As to there being difference near Wadborough, I'm a bit confused there should be no difference, but not surprised that there might be - A similar issue happened last month. It transpired that the reason then was a result of mapping suite defaults and the user reducing the navigation point-count.
I would strongly advise caution using the Westgate island, it's there (as are all other roads/paths, but avoided following RA). You will be competing with traffic travelling at potentially motorway speeds and trying to cross lanes, but it's your choice* (*which I completely respect). I would add that if it is used, you also have the main inner ring road to navigate as well.
For those that don't have the ego-chase of trying to get their "best 300 time", the A38/A40 roundabout can be missed if you take the lane through Sandhurst. It will mean that you cover a whole extra kilometre, but it is very peaceful.
If you've decided to use the A38 for your approach to Gloucester, you might consider ploughing straight up Bristol Road, and up Southgate street over the cross and down Northgate street. Then left into Worcester street, go straight on at the roundabouts, this will get you on to the A38 out of Gloucester heading north. BUT PLEASE CHECK the status of Northgate & Southgate streets in the city centre. They are pedestrian zones at certain times of the day. And they are monitored quite stringently.
And finally to answer the most commonly asked question. I've ridden the route and finished comfortably inside twelve hours, but on the first running of the event, I recall that just about everyone sat on my wheel until we got to the Severn bridge crossing (approximately 240km), I was absolutely shattered by then, and stayed at the last control until 11pm, getting back to arrivee with an hour or so to spare. That ride was very windy, and I was the mobile wind-brake for the day.