Having the ability (because of owning them) to use a Summit (without rotisserie burner), an old style Genesis II (which has the EW burner design so is arguably better at rotisserie), an old Ducane gas with a conventional rotisserie burner (not infrared) and a 6 burner Wolf grill with an infrared rotisserie burner, I will give you my true experience since rotisserie is one of my favorite things.
I will rate the grills in order of rotisserie performance and more importantly WHY I rate them this way.
#1 The ugly old Ducane 2004 model. the conventional burner on it also features a wood chip tray just above the burner. Rotisserie done on this (with or without chips) is amazing. Perfectly browned moist and succulent. It does an amazing job. It is actually the only reason I keep the grill around because as a "grill" it is not very good.
#2 The Wolf. Like the Ducane because the burner is in back of the food there is never a worry of flare up, gravies are easy to make as the drippings do not burn in the catch pan. As to why #2? Well the grill is so enormous (I truly think I could fit an entire small pig in there) and because the burner is infrared the heat getting in to the meat varies tremendously by the size of the roast. IOW the larger diameter of the food the better the performance. Well I don't usually cook enormous cuts of meat so the meat surface tends to be so far away from the heat source it does not perform as well as the Ducane. Trust me though it is still LIGHT YEARS better than my last choice.
#3 The old style Genesis. The beauty of this grill is being older it has the very deep firebox plus the E/W burner design (IOW the tubes run from left to right rather than from front to back). In some ways this actually beats the Wolf but with one disadvantage. Because the burner(s) are positioned under the meat some flare up does happen if not careful (especially on large roasts like beef standing rib) which can if not careful cause an off flavor in the meat. Also it is more difficult to save drippings for gravy. But again despite the shortcomings still light years ahead of last choice
#4 the Summit. Now a disclosure. Yes the Summit is nowhere near as good at this than it's companions BUT it WILL turn out a respectable result so is definitely not to be misconstrued as BAD. Because the Summit has short burners running front to back the heat produced tends to collect and concentrate on the ends of the roast/bird consequently it will not roast as evenly as it's contemporaries which have burner(s) running across the meat (same direction of the rotisserie rod) and that is truly the secret to turning out the best rotisserie product (even more important than the type of burner infrared vs conventional).
So there you have it. I own and use every grill I mentioned here on a regular basis. So while I can turn out wonderful product on any of them one type will stand out as better always and easier to produce reliable consistent results.
So my opinion is if the 620 does NOT have a rotisserie burner and you REALLY want top notch rotisserie don't buy it. Buy the 670. You will not be sorry you did. Note; I cannot comment on a "sear station" nothing I own has one so for that I cannot help.
Best of luck!