I can't see his peak being better than Jagr's or McDavid's or Kucherov's or MacKinnon's. Then, there's Messier, Yzerman...
Gilmour certainly had an outstanding 1992-93 and a very good 1993-94... but these get a little overblown because Toronto. (His scoring finish in 1987 was higher than in 1993.) His ES production in 1992-1994 was about the same as with 1987 St. Louis or c.1989-1991 Calgary, with the difference being overall ice-time and PP time. In Calgary, he'd been effectively used as a second-liner and had to share PP time with Nieuwendyk, etc.
I mean, what is Gilmour's peak anyway? Is it just 1992-93? In 1993-94, he scored 98 points in the final 78 games, which, considering ice-time increase and PP increase, probably puts his production (per-60 or whatever) below 1990-91 Calgary and maybe 1986-87 St. Louis.
1992-93 was a "peak of peaks", I guess, but I'd say his peak is basically spring 1986 to spring 1994. And it would be a hard sell to say that peak is better than the six guys I listed above (not to mention Lindros, Fedorov, Kane, etc., etc...).
Note: I should add that one thing I like about Gilmour is that he really brought it in the playoffs. Good playoff performer, consistently! (We'll overlook his game four vs. L.A. in 1990 and his brutal gaffe in the first period of game 7 vs. the same team in 1993...)