with regards to gabapentin - i think it depends alot your metabolism and drug use in the past.
first time i had gabapentin i had 2000mg and got a drunk/juiced feeling, but was more of a clumsy sedated feeling.
slept well that night, but tolerance builds fast and if you have done alot of drugs in the past, 600mg may not even be noticeable.
i think my abuse of G over the years has broken a few areas related to GABA so may be a reason for my tolerance to benzos and stuff like gabapentin.
lyrica is a different story, but much more expensive.
i find 1200mg will be enough to make my xanax a bit more sedating and better for sleep - but 1200mg on its own does nothing.
do remember they take upto 2 hours to fully be effective, so you just need to hang in there a bit lol
i did have a fair trippy night recently where i took 2000mg of gabapentin, waited 1.5 hours, had 6 travacalm HO, 15 nurofen plus and washed it down with 2 beers, waited 15 minutes and had 2mg of xanax.
had complete awake style black out, woke up next to a few random cut cables (phone charger, USB cord etc) and would say shit mid conversation even if no one was talking and it wouldn't make sense anyway.
my mrs caught me standing next to the toaster with some tongs and i claimed to be trying to clean it with said tongs lol
but back on topic slightly, gabapentin then some codeine plus a benzo is quite a nice mix - dunno bout a 'trip' but was a very relaxed, calm and sedated feeling which eventually lead to a very good sleep with no grogginess in the morning.