The version installed from the original DVD is 4.07
Here you can find the patches to later versions.

The "4.10.1 Mega"-patch and "4.11.1 ultra"-patch are "all-inclusive", so you don't need the previous versions..
but they are linked below, just in case You might need them, for example 4.09 to Ultrapack2.01 and 4.10 for UP3.
(What i mean is, that you don't need to download 4.08, 4.09, 4.10.1 MEGA AND 4.11.1 ultra, just the ULTRA is enough if you want to run 4.11.1 Official.)

[ ]il2_1946_408m.exe145 MiB
[ ]2_4.09 Patch torrent pack.zip131 KiB
[DIR]4.09 Game Patch EN/ ->
[ ]IL-2_MegaPatch4.10.1m_EN.rar994 MiB
[ ]il2_4.11.1_ultra.exe1,96 GiB

Enjoy, Clear skies and good hunting!

-Juuba