For what it's worth, I've played 7 games so far against tournament-caliber opponents, RPIs 5, 7, 8, 12, 12, 13, and 39. I'm 3-4 in those games, with 1 win and 2 losses coming in OT. More to the point, Vegas has been held to "only" 16.6 PPG in these contests. Part of this is because we've run normal tempo in 4 of those games as opposed to uptempo in most or all of the rest. The major factor, though, is that his shooting, not surprisingly, drops off.
On the one hand, he's still shooting 50% on deuces against tournament-caliber opponents while dropping to 37.5% on 3s. This still slightly favors the 3-ball on a PPS basis with fouls not included, it's much closer. On the other hand, he's only attempting 2.7 FTs per game. Not a huge surprise that a 41/61 Ath/Spd guard has a tough time drawing a lot of fouls against better defenses. Those stats seem to suggest that an approximately equal ratio of 2s and 3s (which is maintained in the higher-caliber contests, with 48 of each) is about right against tougher opponents. So maybe for now I shift him to +2 but bump him back down to +1 come tournament time...