Nick,

  I'm going to answer both your C-41 and RA-4 questions here.

  It depends upon what the manufacturer of the chemicals recommends.

  For both RA-4 and C-41, I use Tetenal ColorTec Professional chemistry.
In both set's of instructions it specifically says not to pre-soak.  It does
include instructions for Rotary Processing.  The reason they give is because
the residual water will dilute the developer and provide a shift in
processing.  When you consider two things:  a.  the amount of water carried
forward tot he developer will never be consistent, and b.  the RA-4
development time is so short that a slight deviation is more than likely to
have an effect, I'll follow the chemistry manufacturers instructions and
leave Jobo's well intended advise foe those who choose to experiment.

Jim

I came up with a way to aviod pre-soak, and it seems to work ok.

I don't have a jobo for my RA4/C41 - I use an old unicolour roller
base that rotates, and gives even agitation.

I like to process RA4 at 95 rather than 75, so to keep temperatures up
I put a 30W incandescant spotlight on the tube as it rotates. The
spotlight is on a gooseneck, and is placed 2-3" off the middle of the
tube.  It is controlled by the same timer that runs the motor base.
If you leave the light stationary on the tube for more than a short
time the plastic will begin to bubble and soften...

This keeps the outside of the plastic tube warm, so the chems don't
cool off too much as they roll about.

for C41 I use the paper tube and roller base too.

I have 2 high or 4 high steel tanks for film.  To get consistent
agitation::

Load the film reels, and put them in the dry tank, and put the lid on

Warm up the paper roll by pointing the spotlight down the middle of
it.  After about 2 minutes I flip the tube to the other end, so the
tube warms a bit more evenly.

stand at the sink, get the developer, paper roll, and tanks, and
somewhere dry to set the loader reels ready.

In total darkness take the rolls out of the tank, set aside, pour the
pre measured right amount of heated developer into the tank, drop the
loaded reels back in, put the daylight lid back on the tank, and
swithc the lights on.  Put the daylight tank inside the warmed roll,
and put it on the agitator base.

It sounds like a lot, but it is all done in 15 seconds. Let the tank
roll for 2:45; this gives 15 seconds at the end for drain time, before
you pour the stop bath in.

The rest of the process needn't use the roller base, as they are not
as critical on precise time and agitiation control, but by doing so
the longer steps your hands are free to rinse up containers and tidy
from earlier steps in the process

Using the steel tank directly on the roller base doesn't work, because
the tank is too small around to fit the rollers.

If you wanted to use a lot of chems you could use the tank on its own
( this is an option to sheet film developers), however you loose the
ability to use the outer plastic sleeve as a pre-warmed insulator.

If you use the paper sleeve on its own, then run a water phase first
to see how cooler it comes out than it goes in, and you can then guess
at how much longer to extend development time.