Why not get a top end porty? They will have similar performance to an electric tm and probably cheaper to buy and maintain.
 They say a PD blower doesn't loose as much cfm/lift under restriction as electric vacs  ...
 A 5HP electric motor on a 33 blower would have only about 10hg and 160 cfm  compared to an airflex Storm  which has 9hg and up to  290 cfm .
But under working conditions , where the wand meets the carpet , its said the electric vacs performance dips below that of the blower based system .
Just stating what iv read , its difficult to measure ...  i think the guys on TMF have come up with a sophisticated test ...  the 5 gallon bucket test !   after 100ft of hose dip the hose in the bucket of water and measure time to empty .  

Having said that ,iv read that mytee tested a 5hp pd blower etm and concluded that their electric vac etm  ( i presume they mean the quad version ) gave better vacuum .  But there could be more to that also , cost to produce , shipping weight etc ..