If we're talking about sub-sonic aircarft, would I be right in saying then that a compromise needs to be reached...
In sweeping the wings back to enable Mcrit to be increased, a concession is made with respect to the amount of lift produced, as the swept wing has a lower lift coefficient than a rectangular one. The faster the aircraft goes (in terms of mach number), the more the wings have to be swept back to delay shock waves being formed. A certain amount of lift is required for an aircraft at a certain weight, so the wings can't be swept back too much otherwise this lift won't be produced (keeping all other things constant). With extra sweep, you would therefore need to travel faster, which would then require more sweep to delay the shockwaves ...and the viscious circle continues...
Is it just a question of finding (well, getting the engineers to figure out)the optimum angle of sweep to meet the requirements of cruising at a certain sub-sonic mach number, at a certain weight?