But your "question' is really 6... so I numbered them to address each individually.....
1) 99% of 1725rpm motors can run 3000rpm a-ok - do it!
2) no more, no less: exactly the same. 3hp motor will produce 3 hp from 1725 to 3000rpm.
3) heat will be the same from 1725 to 3000rpm.
5) I dont understand ur use of the word gear..... sorry. see #6 tho.
6) torque produced will be 9#-ft from some low speed like 300rpm upto 1725rpm. then torque will go down linear as speed goes up to 3000rpm for constant hp.
great questions Ozzie!