Hi Ian, I've just opened a topic as I'm having roaming issues. That said, you should be able to roam seamlessly. However this depends on a number of factors, is this an Intra-Controller Roam or Inter-Controller Roam? If you roaming between controllers, does the client keep the same IP (L2) or is the client roaming is a new subnet (L3). If so then Mobility needs configuring. If not then you should be okay with Fast-Failover/Session Availability. Other factors that will dictate roam time includes the type of SSID WLAN configured, is there a RADUS server involved? This will add more of a delay over an Open or WPA2 SSID.
Another thing to consider is using all of the 5GHz channels, the DFS channels can force a client to drop if a RADAR is detected. Additionally some clients don't support all of the 5GHz channels.
Make sure you client drivers are up-to date that can help.