I think 175 overrates Al Boum Photo by 5-8lbs and I think Champ is capable of a high 170s performance if able to fully express himself with fitness, jumping, run of the race etc.
It’s probably Champ’s one and only chance to run to that level as he’ll be into double digits next year. I also suspect, given his pedigree and niggly wind issue (family of Best Mate, Cornish Rebel etc) that better ground would enhance his chance. It’s to his huge credit that he could win the RSA last year despite soft ground, a pretty dreadful round of jumping and possibly gurgling if Hendo is to be believed.