i have been posting basically the same thing for years. search this topic and read my older posts.

actually DOT 4 & 5 don't MIX. mixing the 2 won't cause then to jell either..
do a at home test yourself. get a jar and mix the 2. DOT5 is usually purple and DOT is clear to almost clear. shake well and let then sit. after a while the 2 products will be at different levels in your jar. it will stay this way as long as you keep this jar.
they also have slightly different compression rates so this can give you a odd brake pedal feel when mixing the 2 products.
also don't just top off DOT 4 with DOT 5 or vice versa. doing this will create problems in brake performance. this is probably why these rumors started.

you can use 5 and force out the 4 NO PROBLEM without flushing with alcohol. i did this every time i switched from 4 to 5.

actually flushing with alcohol will create some problems by itself.

the most important thing to remember when using DOT 5 is it easily retains AIR. this is why it has a bad reputation as a poor product.
this is why you can't use it in a anti lock braking system.

a few thoughts when using DOT 5 brake fluid.
don't shake up the bottle before you use it.
i like to open the bottle and let it sit out in the sun for a hour or so before using. this will help force the air out of the fluid before using.
when bleeding don't pump the pedal fast. pump slowly and constantly.

another thing to keep in mind when using DOT5. because water doesn't mix with it. because of this you can develop water pockets inside of your brake lines. this can also create a set of problems with pedal feel and lines rusting from the inside out.
you might want to consider changing DOT 5 every few years if you plan on switching fluids.

hope these tips help.