We have the H & M - with heat to 150 degrees Celsius, I have a clip on hotbox and also a single operator and twin operator dry steam machines. These are 180 degrees Celsius.
Our work is on well known supermarkets and though the dry steam machines are slower they definitely have their place.
A lot of our work is in live environments, with passing footfall and there would not be any chance of using a hot pressure washer.
The pros and cons are -
Hot is quick, can cause damage in the wrong hands and cannot be used in live environments, no chemical is required (most of the time) and there is no messing around changing machines over.
Steam - I have found that the machines do not travel well and the first thing we do is reconnect small pipes that have come apart, you may need a generator for power or will have a trailing supply lead, they are slow, the chemicals are expensive, the brass heads work out at about £3.00 each ($4.69) and you can go through them on a good day.
The good bits are that it is difficult to cause damage to the surface, the work is relatively easy and the end result is always excellent (with no residue) and is much better paid.
The chewing gum removal work in the UK is difficult to gain - we do so much of it because of who we work for. I don't know what the regs are over there but here it is something like - If gum is raised it must be removed within two years, once flattened it is no longer considered rubbish and is ignored.
We have a massive problem with it and I am pushing this side of the business because it is such a UK wide issue!
Good luck
Rob