I can't say I'm experienced with this combo, but I have just experimented with it yesterday. Time log (not real time) and all for your convenience.
11:15-I ingested 4 pills of 50mg 5-htp+some alfalfa. I was sitting for someone trying salvia for the first time while waiting for 5-htp to kick in.
12:30-I start feeling "dreamy", so I prepare a hookah with good pile of bag-bottom shake and some apple-flavoured tobacco.
13:00?-Pretty normal for weed
-Here I lost track completely, wrote some insane shit, listened to music, meditated, etc.-
16:00- Pretty close to baseline, was very fun and quite introspective. Visual distortion was enhanced, more immersive mentally, but also more tension maybe? I don't normally grind my teeth when high...
21:30- I go to sleepand went to sleep; I'm tired, but not burnt out.
5:45 this morning- I wake up very refreshed, not dehydrated as I usually do (even without pot, I probably sleep with my mouth open because it's parched every morning).
So all in all, I think 5-htp made the high more introspective and more tense, but also worked more to attenuate the adverse effects. I usually wake up late and tired if I smoke in the day, and with 5-htp my sleep was deep and refreshing.