I don't see something special. Try with another game, it's perhaps a game that need special config or not compatible.
The only difference I have.
Dreamcast.RTC=1543195063
don't know what is it.
PatchRegion=1
LoadDefaultImage=1
No chnage on performance, just in loading iso with command line
But I have made differently for mapping
Current_maple0_5=PuruPuru_Win32.dll:0
Current_maple0_0=drkMapleDevices_Win32.dll:2
In port A, I m selecting "purupuru Controller" and inside it, I m selecting "NullDc VMU"
My config >
http://pastebin.com/8tuMaHPaBut I don't thing your mapping can decrease performance, make a try with another game.