After some testing, I have found that SNMPWalk is considerably slower than multiple SNMPGet.
I was aiming to retrieve 6 Objects from a MIB; the device being polled was attached via a 100mbps network link.
I decided to run SNMPGet within a loop to retrieve each Object from the specified OID's.
As these OID's were within the same tree, I then thought about using walk as this would consolidate the data into a single request. I then walked the tree to get the same result.
I subsequently testing the time it took to retrieve this information via microtime().
As a result, you can retrieve 1 walk containing 6 OID's within the same time as requesting 18 OIDs via get.
I hope this helps someone whom is looking to speed up their SNMP requests.