Well, Hermes provides realistic advice, it is possible to improve your VAM. I reviewed my Garmin and Strava data from this month I have the following results. Keep in mind this is on a 26 lb flatbar fully rigid touring bike.
I have three different climbs this month with >1000 VAM numbers. For example: 290 ft climb over 0.29 miles, a 18% grade taken at 6.0mph for a 1167 VAM.
The Strava data can be found here:
https://www.strava.com/activities/2363955957
My VAM as posted by Strava is usually in the 500-600 range, I'm a little suspicious of a result better than this.
I have an event in June that features several difficult climbs. I'll be using a Ridley Helium SLX with a 46 & 30 Absolute Black chainring set. I'll check back after this event.