I should of course say straight out that taking a rec. dose of G while on a rec. dose of a benzo, or vice versa, will cause you to pass out at best.
However, several months ago, SWIM developed a technique for GBL WD (I can't account for GHB as this has not been tried and the slower onset could alter the outcome) that minimises the consequences of taking high dose benzo's in G withdrawal (massive cognitive impairment and anterograde anmesia on top of those withdrawal symptoms that cannot be controlled by benzo's like the shakes and the sweats.), avoids the extremely unpleasant G tapering process and allows maximum possible functionality of the individual in the process. This method has been tried on 4 people successfully.
A moderate amount of diazepam (preferably, or any other benzo with long half life, say 20mg equivalent) is taken around 15 minutes before G WD's are expected to develop (time of dose will vary based on the individual - I'm using a 20 minute onset period for an example here). Subsequently you wait until a point where the WD's overpower the effect of the benzo - NB - UNBEARABLE, at which point you take 1/8th of your standard G dose. Wait for 15 minutes to see if they become bearable again and if not take another small G dose, more or less than an 1/8th depending on how effective that was, but no more than 1/3rd. Once again, wait until they become unbearable and repeat WITH EXTREME CAUTION. It will eventually become necessary to take a further dose of benzo. I'd recommend no more than 30 -40mg diazepam equivalent per day. Bear in mind that due to the long half life diazepam can build up in the system over time
As time passes the necessary doses of GBL and benzo can be reduced, and the duration between doses can be extended until GBL WD is no longer noticable and dosage of GBL can be discontinued altogether, and then the benzo should be tapered down ASAP. The GBL taper should be expected to take 1-2 weeks with the same amount for the subsequent benzo taper, if not less.
I'd recommend seeking the assistance of another person to give you the doses if you're an individual with poor self control.
DISCLAIMER: This technique has only been tried on a few people and although successful so far it does need a fair degree of self control as compared to a straight benzo WD. SWIM accepts no responsibility for anyone who doesn't have success and should once again point out the EXTREME CAUTION a person should use when mixing CNS depressants. Taking too much of either will at best make you pass out and could at worst leave you in a coffin. But as WD processes go, this has been the most effective for SWIM.