Well, considering that with a propane burner you are only utilizing about 36% (ala Sacc.) of the BTUs that the burner produces... most electric elements are right up there.
I can reach a boil in under 8 minutes easy with 5500W. That equates to only 18,700 BTUs... yah, 18,700. This equates to the performance of a 52,000 BTU propane burner.
I dont know why you do not boil over anymore... because I can easily boil over my 15.5 gal sankey while doing a 5 gallon batch with electric. I have done it on my brewcasts...
I use 100% to reach the boil, 70% to maintain it at 3700W or 12,580 BTUs
People are under the incorrect assumption that electric applies much fewer BTUs than gas, when that is simply not true. There is a reason your garage heats up to 90+ degrees in the winter when boiling with gas, you are wasting a crap ton of BTUs that arent going into the wort. When using electric, you are placing the BTUs directly in the wort, super efficient, cold garage. A 52,000BTU burner is the same as a 5500W element basically. Pretty amazing.