Here is a thread with my experience using Jim's method of the lowest flash boiling temperature to set the offset.

Profitec Pro 600 Owner Experience

I don't think you can generalize an offset for 'e61'. Very few are identical. HX/DB, internal plumbing, gicleur geometry, sensor, etc. and the PID all effect what the offset will be.

I had 2 identical Vibiemme e61 groups, one on an HX with ≈22°F offset [Delta PID] and another on a DB w ≈20°F offset [Gicar]. I also serviced an identical Vibiemme HX with Auber PID and it required a ≈13°F offset.

I never saw the point in having an offset on an HX. It's not linear so you need a table to adjust.

salmotrutta wrote:<snip>Curious what other E61 users use as their set temp, and if anyone has measured the offset at the group head.

The question isn't specific enough to provide a definitive answer. A great deal depends on what sort of e61 machine one has and how one uses it.
On a DB, one can adjust the brew boiler offset so that the brew water temperature is as desired. To my mind, a PID on a DB makes good sense. The manufacturer sets the offset for typical use. For most of us, that may be good enough. But, for the truly fussy, it would make sense to measure the brew water temperature and adjust the offset accordingly. You may find that the desired setting is different depending on the number of shots pulled...just two at a time, you and the missus, vs a house full of guests. The e61 is reasonably stable on a DB machine for a couple of shots, but you may want to check it out for larger volume, and either set the PID accordingly, or develop a temperature recovery technique, or both.
On an HX, with few exceptions, a PID, in my opinion, is about as necessary as providing a bicycle for a fish. Proper brew temperature management involves flushing. That said, if one only uses it to pull shots and not steam milk, then the PID would be useful; one could almost treat an HX used for shots only like the brew boiler of a DB machine. Of course, if you ever do want to steam properly, then the temperature has to go way back up. In essence, the machine becomes like a SBDU, used this way. It also depends on whether the HX is a dragon (most older designs) or if it's tamed with a restrictor or other means , like the Mara.

Nunas wrote:On an HX, with few exceptions, a PID, in my opinion, is about as necessary as providing a bicycle for a fish. Proper brew temperature management involves flushing.

Properly implemented a PID on an [e61] HX makes perfect sense.

1. It's more energy and water efficient
2. It's quieter
3. Precise walkup shot temperature is maintained and it's quickly and infinitely adjustable
4. It's cost effective relative to two boilers

Implemented with a pstat or dual setpoint PID for steaming, by the time the puck is prepped, the boiler will be at steam temperature. The thermal mass of the e61 keeps the temperature rise reasonable. Without a dual mode, it's a few seconds to run the PID up to steam temperature and a couple of minutes to reach steam pressure while the puck is prepped.

I ran a Vibiemme with PID & pstat for 15 years. I could make 5 latte and still enjoy my shot as the brew temperature had risen only slightly. No flushing ever required. See HX Heaven or 1½ Boiler