There is no table but it would be nice if aruba made one... i get that question asked MANY times as well...
Ill give you some highlights
1-One cluster of instant are just able to support 1024 users... but if you using a cluster of IAP 92/93 it just go up to 16 APS and 256 users other instant can go up to 1024 users... so its limited
2-Captive portal with the controller is a way better, because on the captive portal of the Instant is really really basic... you must manually delete users you create, and also the captive portal page is not that cutumizable.
3-Controller has VPN terminator, which mean it can do RAPS and VIA, if you going for this, you cannot sell them IAPs.
4-Controller simplifies vlan at edge i do not need to tag the vlans everywhere
5-You are able to change more advanced settings on the controller than you can do it on the instant.
The thing is like Collin told me before, is that the differences between Instant and Controller-Based Deployments decrease all of the time.
The major difference i think are the ones i told you up at least thats what i think. Anyways remenber that you can always go from instant to controller anytime you want, so if they on the run need something that is just avaiable on the controller they can get one and transform all those IAPS in normal campuses APs.
Hope it helps
Cheers
Carlos