Yes - PE4's were longer than PE1's as Hugh says...

but the new PE4 cards now available have cooling fans onboard and are shorter than the original PE4's... and their part code ends in 'H'

best way to check is to read the lable on the back of the board (not the small mez board) It should show the main card serial number, and the product code - then ending with PE1 or PE4

eg:
AS-PHX-D10HDSDI-PE1
this is a Phoenix Simgle HD-SDI input PE1 1x lane card

AS-PHX-D20HDSDI-PE1
this is a Phoenix Dual HD-SDI input PE1 1x lane card

AS-PHX-D20HDSDI-PE4
this is a Phoenix Dual HD-SDI input PE4 4x lane card

AS-PHX-D20HDSDI-PE4H
this is a Phoenix Dual HD-SDI input PE4 4x lane half size card with fan (new version)

There 'should' be no difference in performance or driver requirements between the the PE4 & PE4H cards - except that it runs cooler...

S